Encoder, a decoder and corresponding methods for inter-prediction

ABSTRACT

An inter-prediction method and apparatus are provided. An initial motion vector is obtained for a current block. Search space positions are determined according to the initial motion vector. Matching costs for the search space positions are checked according to a checking order to select a target search space position with a minimal matching cost. A refining motion vector of the current block is determined based on the initial motion vector and the target search space position. A central search space position is determined first according to the checking order, and the central search space position is pointed to by the initial motion vector.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2019/126977, filed on Dec. 20, 2019, which claims priority to U.S.Provisional Patent Application No. 62/812,190, filed on Feb. 28, 2019,the disclosures of the aforementioned applications being herebyincorporated by reference in their entireties.

TECHNICAL FIELD

Embodiments of the present application generally relate to the field ofpicture (image) processing and more particularly to inter-prediction.

BACKGROUND

Video coding (video encoding and decoding) is used in a wide range ofdigital video applications, for example broadcast digital TV, videotransmission over internet and mobile networks, real-time conversationalapplications such as video chat, video conferencing, DVD and Blu-raydiscs (data storage and decoding), video content acquisition and editingsystems, and camcorders of security applications.

The amount of video data needed to depict even a relatively short videomight be substantial, which may result in difficulties when the data isto be streamed or otherwise communicated across a communications networkwith limited bandwidth capacity. Thus, video data is generallycompressed before being communicated across modern daytelecommunications networks. The size of a video could also be an issuewhen the video is stored on a storage device because memory resourcesmay be limited. Video compression devices often use software and/orhardware at the source to code the video data prior to transmission orstorage, thereby decreasing the quantity of data needed to representdigital video images. Compressed data that is transmitted is received atthe destination by a video decompression device that decodes the videodata. With limited network resources and ever-increasing demands ofhigher video quality, improved compression and decompression techniquesthat improve compression ratio with little to no sacrifice in picturequality are desirable.

SUMMARY

A scheme for constructing a search space for motion vector refinement isprovided, several checking orders for checking the matching costs of thesearch space positions in the search space is illustrated in the presentapplication. Embodiments of the present application provide apparatusand methods for encoding and decoding according to the independentclaims.

In a first aspect of the present application, an inter-prediction methodcomprises obtaining an initial motion vector for a current block;determining search space positions according to the initial motionvector; checking matching costs of the search space positions accordingto a checking order to select a target search space position with aminimal matching cost; and determining a refining motion vector of thecurrent block based on the initial motion vector and the target searchspace position, wherein a central search space position is checked firstaccording to the checking order, and wherein the central search spaceposition is pointed to by the initial motion vector.

In an implementation, search space positions comprise the central searchpositions and neighboring search space positions, wherein determiningsearch space positions according to the initial motion vector, comprisesdetermining the central search space position according to the initialmotion vector; and determining the neighboring search space positionsaccording to one or more preset offsets and the central search spaceposition.

In an implementation, a search space consists of the search spacepositions, and a pattern of the search space is a 5×5 search spaceposition square.

In an implementation, checking matching costs of the search spacepositions according to the checking order to select a target searchspace position with a minimal matching cost, comprises checking a matchcost of each of the search space positions in turn according to thechecking order; and selecting a search space position with the minimalmatching cost among the search space positions as the target searchspace position.

In an implementation, checking the match cost of each of the searchspace positions in turn according to the checking order comprisescomparing a match cost of one of the search space positions with a tempminimal matching cost; setting the match cost of the one of the searchspace positions as the temp minimal matching cost when the match cost ofthe one of the search space positions is smaller than the temp minimalmatching cost; and setting the temp minimal matching cost as the minimalmatching cost after the last one of the search space positions ischecked.

In an implementation, the central search space position is set as (0, 0)of a coordinate system, horizontal right is set as a horizontal positivedirection and vertical down is set as a vertical positive direction.

In an implementation, the checking order is (0, 0), (−2, −2), (−1, −2),(0, −2), (1, −2), (2, −2), (−2, −1), (−1, −1), (0, −1), (1, −1), (2,−1), (−2, 0), (−1, 0), (1, 0), (2, 0), (−2, 1), (−1, 1), (0, 1), (1, 1),(2, 1), (−2, 2), (−1, 2), (0, 2), (1, 2), (2, 2).

In an implementation, the checking order is (0, 0), (−1, 0), (0, 1), (1,0), (0, −1), (−1, −1), (−1, 1), (1, 1), (1, −1), (−2, 0), (−2, 1), (−2,2), (−1, 2), (0, 2), (1, 2), (2, 2), (2, 1), (2, 0), (2, −1), (2, −2),(1, −2), (0, −2), (−1, −2), (−2, −2), (−2, −1).

In an implementation, the checking order is (0, 0), (−1, 0), (0, 1), (1,0), (0, −1), (−1, −1), (−1, 1), (1, 1), (1, −1), (−2, 0), (0, 2), (2,0), (0, −2), (−2, −1), (−2, 1), (−2, 2), (−1, 2), (1, 2), (2, 2), (2,1), (2, −1), (2, −2), (1, −2), (−1, −2), (−2, −2).

In an implementation, the checking order is (0, 0), (−1, 0), (0, 1), (1,0), (0, −1), (−1, −1), (−1, 1), (1, 1), (1, −1), (−2, 0), (0, 2), (2,0), (0, −2), (−2, −2), (−2, 2), (2, 2), (2, −2), (−2, −1), (−2, 1), (−1,2), (1, 2), (2, 1), (2, −1), (1, −2), (−1, −2).

In a second aspect of the present application, an inter-predictionapparatus comprises an obtaining module, configured to obtain an initialmotion vector for a current block; a setting module, configured todetermine search space positions according to the initial motion vector;a calculating module, configured to check matching costs of the searchspace positions according to a checking order to select a target searchspace position with a minimal matching cost; and a prediction module,configured to determine a refining motion vector of the current blockbased on the initial motion vector and the target search space position,wherein a central search space position is checked first according tothe checking order, and wherein the central search space position ispointed to by the initial motion vector.

In an implementation, search space positions comprise the central searchpositions and neighboring search space positions, the setting modulebeing configured to determine the central search space positionaccording to the initial motion vector and to determine the neighboringsearch space positions according to one or more preset offsets and thecentral search space position.

In an implementation, a search space consists of the search spacepositions, and a pattern of the search space is a 5×5 search spaceposition square.

In an implementation, the calculating module is configured to check amatch cost of each of the search space positions in turn according tothe checking order and to select a search space position with theminimal matching cost among the search space positions as the targetsearch space position.

In an implementation, the calculating module is configured to compare amatch cost of one of the search space positions with a temp minimalmatching cost; set the match cost of the one of the search spacepositions as the temp minimal matching cost when the match cost of theone of the search space positions is smaller than the temp minimalmatching cost; and set the temp minimal matching cost as the minimalmatching cost after the last one of the search space positions ischecked.

In an implementation, the central search space position is set as (0, 0)of a coordinate system, horizontal right is set as a horizontal positivedirection and vertical down is set as a vertical positive direction.

In an implementation, the checking order is (0, 0), (−2, −2), (−1, −2),(0, −2), (1, −2), (2, −2), (−2, −1), (−1, −1), (0, −1), (1, −1), (2,−1), (−2, 0), (−1, 0), (1, 0), (2, 0), (−2, 1), (−1, 1), (0, 1), (1, 1),(2, 1), (−2, 2), (−1, 2), (0, 2), (1, 2), (2, 2).

In an implementation, the checking order is (0, 0), (−1, 0), (0, 1), (1,0), (0, −1), (−1, −1), (−1, 1), (1, 1), (1, −1), (−2, 0), (−2, 1), (−2,2), (−1, 2), (0, 2), (1, 2), (2, 2), (2, 1), (2, 0), (2, −1), (2, −2),(1, −2), (0, −2), (−1, −2), (−2, −2), (−2, −1).

In an implementation, the checking order is (0, 0), (−1, 0), (0, 1), (1,0), (0, −1), (−1, −1), (−1, 1), (1, 1), (1, −1), (−2, 0), (0, 2), (2,0), (0, −2), (−2, −1), (−2, 1), (−2, 2), (−1, 2), (1, 2), (2, 2), (2,1), (2, −1), (2, −2), (1, −2), (−1, −2), (−2, −2).

In an implementation, the checking order is (0, 0), (−1, 0), (0, 1), (1,0), (0, −1), (−1, −1), (−1, 1), (1, 1), (1, −1), (−2, 0), (0, 2), (2,0), (0, −2), (−2, −2), (−2, 2), (2, 2), (2, −2), (−2, −1), (−2, 1), (−1,2), (1, 2), (2, 1), (2, −1), (1, −2), (−1, −2).

In a third aspect of the present application, a method for determining amotion vector to be used in inter-prediction of a current block of avideo picture (or frame). The method comprises obtaining an initialmotion vector; obtaining at least two groups of points (in an example,one group of points may comprise only one point) according to theinitial motion vector; obtaining the motion vector for the current blockaccording to the at least two groups of points and a cost function.

In an implementation, the at least two group of points comprise allpoints that are inside a square, the square is centered at a pointcorresponding to the initial motion vector.

In an implementation, the at least two group of points comprise allpoints that are inside a square, corners of the square are determined bythe coordinates (−2,−2), (2, 2), (−2, 2) and (2, −2).

In an implementation, a first group of points in the at least two groupsof points comprises the center point that is pointed by the initialmotion vector.

In an implementation, a second group of points in the at least twogroups of points comprises four points that are left, top, right andbottom neighbors of the center point, the center point is pointed by theinitial motion vector.

In an implementation, a third group of points in the at least two groupsof points comprises four points that are 1 pixel sample away from thecenter point and that are not comprised in the second group.

In an implementation, a fourth group of points in the at least twogroups of points comprises points that are 2 pixel samples away from thecenter point at least in one coordinate axis.

In an implementation, the at least two groups of points are processedorderly when the at least two groups of points are processed with thecost function.

In an implementation, a fourth group of points in the at least twogroups of points comprises points that are 2 pixel samples away from thecenter point in one coordinate axis and 0 pixel samples away from thecenter point in the other coordinate axis.

In an implementation, a fifth group of points in the at least two groupsof points comprises points that are 2 pixel samples away from the centerpoint at least in one coordinate axis and that are not included in thefourth group of points.

In an implementation, a fifth group of points in the at least two groupsof points comprises points that are 2 pixel samples away from the centerpoint in both −x and −y coordinate axes.

In an implementation, a sixth group of points in the at least two groupsof points comprises points that are 2 pixel samples away from the centerpoint at least in one coordinate axis and that are not included in thefourth or the fifth group of points.

In an implementation, a fourth group of points in the at least twogroups of points comprises points that are 2 pixel samples away from thecenter point only in one coordinate axis and 0 pixel samples away fromthe center point in the other coordinate axis.

In an implementation, when one group of points in the at least twogroups of points comprises at least two points, the points of the groupare ordered according to a predefined rule.

In an implementation, when one group of points in the at least twogroups of points comprises at least two points, the leftmost point amongthe group of points is selected as the first point among the group ofpoints.

In an implementation, when one group of points in the at least twogroups of points comprises at least two points, and when there are morethan one point that are leftmost points of the group of points, thepoint that is left-most of the group and that has a coordinatedisplacement that is closer to 0 in vertical direction (−y direction) isselected as the first point among the group of points.

In an implementation, when one group of points in the at least twogroups of points comprises at least two points, and when there are morethan one leftmost points in the group of points and if the points havesame displacement in −y direction, then the left-most point in the topdirection is selected as the first point of the group of points.

In an implementation, when one group of points in the at least twogroups of points comprises at least two points, and after the firstpoint in the group of points is determined, the remaining points in thesame group are ordered based on clock-wise or counter-clockwise scanningof points around the center point.

In an implementation, the initial motion vector corresponds to a motionvector that is derived using an index signaled in the bitstream.

In an implementation, the initial and the obtained motion vector are notcoded into the bitstream.

In a fourth aspect of the present application, a computer programproduct comprising program code for performing the method according tothe first or third aspect when executed on a computer or a processor.

In a fifth aspect of the present application, a decoder is providedcomprising one or more processors; and a non-transitorycomputer-readable storage medium coupled to the processors and storingprogramming for execution by the processors, wherein the programming,when executed by the processors, configures the decoder to carry out themethod according to the first or third aspect.

In a sixth aspect of the present application, an encoder is providedcomprising one or more processors; and a non-transitorycomputer-readable storage medium coupled to the processors and storingprogramming for execution by the processors, wherein the programming,when executed by the processors, configures the encoder to carry out themethod according to the first or third aspect.

In a seventh aspect of the present application, a non-transitorycomputer-readable medium carrying a program code which, when executed bya computer device, causes the computer device to perform the method ofthe first or third aspect.

The foregoing and other objects are achieved by the subject matter ofthe independent claims. Further implementation forms are apparent fromthe dependent claims, the description and the figures.

Details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following embodiments of the application are described in moredetail with reference to the attached figures and drawings, in which:

FIG. 1A is a block diagram showing an example of a video coding systemconfigured to implement embodiments of the application;

FIG. 1B is a block diagram showing another example of a video codingsystem configured to implement embodiments of the application;

FIG. 2 is a block diagram showing an example of a video encoderconfigured to implement embodiments of the application;

FIG. 3 is a block diagram showing an example structure of a videodecoder configured to implement embodiments of the application;

FIG. 4 is a block diagram illustrating an example of an encodingapparatus or a decoding apparatus;

FIG. 5 is a block diagram illustrating another example of an encodingapparatus or a decoding apparatus;

FIG. 6 is a block diagram illustrating another example of a predictionmethod;

FIG. 7 is an illustration of a checking order;

FIG. 8 is another illustration of a checking order;

FIG. 9 is another illustration of a checking order;

FIG. 10 is another illustration of a checking order;

FIG. 11 is another illustration of a checking order;

FIG. 12 is another illustration of a checking order;

FIG. 13 is another illustration of a checking order;

FIG. 14 is another illustration of a checking order;

FIG. 15 is a block diagram showing an example of a prediction apparatusconfigured to implement embodiments of the application;

FIG. 16 is a block diagram illustrating an example of an encodingapparatus or a decoding apparatus;

FIG. 17 is a block diagram showing an example structure of a contentsupply system 3100 which realizes a content delivery service;

FIG. 18 is a block diagram showing a structure of an example of aterminal device.

In the following identical reference signs refer to identical or atleast functionally equivalent features if not explicitly specifiedotherwise.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, reference is made to the accompanyingfigures, which form part of the disclosure, and which show, by way ofillustration, specific aspects of embodiments of the application orspecific aspects in which embodiments of the present application may beused. It is understood that embodiments of the application may be usedin other aspects and comprise structural or logical changes not depictedin the figures. The following detailed description, therefore, is not tobe taken in a limiting sense, and the scope of the present applicationis defined by the appended claims.

For instance, it is understood that a disclosure in connection with adescribed method may also hold true for a corresponding device or systemconfigured to perform the method and vice versa. For example, if one ora plurality of specific method steps are described, a correspondingdevice may include one or a plurality of units, e.g. functional units,to perform the described one or plurality of method steps (e.g. one unitperforming the one or plurality of steps, or a plurality of units eachperforming one or more of the plurality of steps), even if such one ormore units are not explicitly described or illustrated in the figures.On the other hand, for example, if a specific apparatus is describedbased on one or a plurality of units, e.g. functional units, acorresponding method may include one step to perform the functionalityof the one or plurality of units (e.g. one step performing thefunctionality of the one or plurality of units, or a plurality of stepseach performing the functionality of one or more of the plurality ofunits), even if such one or plurality of steps are not explicitlydescribed or illustrated in the figures. Further, it is understood thatthe features of the various exemplary embodiments and/or aspectsdescribed herein may be combined with each other, unless specificallynoted otherwise.

Video coding typically refers to the processing of a sequence ofpictures, which form the video or video sequence. Instead of the term“picture” the term “frame” or “image” may be used as synonyms in thefield of video coding. Video coding (or coding in general) comprises twoparts: video encoding and video decoding. Video encoding is performed atthe source side, typically comprising processing (e.g., by compression)the original video pictures to reduce the amount of data required forrepresenting the video pictures (for more efficient storage and/ortransmission). Video decoding is performed at the destination side andtypically comprises the inverse processing compared to the encoder toreconstruct the video pictures. Embodiments referring to “coding” ofvideo pictures (or pictures in general) shall be understood to relate to“encoding” or “decoding” of video pictures or respective videosequences. The combination of the encoding part and the decoding part isalso referred to as CODEC (Coding and Decoding).

In case of lossless video coding, the original video pictures might bereconstructed, i.e., the reconstructed video pictures have the samequality as the original video pictures (assuming no transmission loss orother data loss during storage or transmission). In case of lossy videocoding, further compression, e.g., by quantization, is performed, toreduce the amount of data representing the video pictures, which cannotbe completely reconstructed at the decoder, i.e., the quality of thereconstructed video pictures is lower or worse compared to the qualityof the original video pictures.

Several video coding standards belong to the group of “lossy hybridvideo codecs” (i.e., combine spatial and temporal prediction in thesample domain and 2D transform coding for applying quantization in thetransform domain). Each picture of a video sequence is typicallypartitioned into a set of non-overlapping blocks and the coding istypically performed on a block level. In other words, at the encoder thevideo is typically processed, i.e., encoded, on a block (video block)level, e.g., by using spatial (intra-picture) prediction and/or temporal(inter-picture) prediction to generate a prediction block, subtractingthe prediction block from the current block (block currentlyprocessed/to be processed) to obtain a residual block, transforming theresidual block and quantizing the residual block in the transform domainto reduce the amount of data to be transmitted (compression), whereas atthe decoder the inverse processing compared to the encoder is applied tothe encoded or compressed block to reconstruct the current block forrepresentation. Furthermore, the encoder duplicates the decoderprocessing loop such that both will generate identical predictions(e.g., intra- and inter-predictions) and/or re-constructions forprocessing, i.e., coding, the subsequent blocks.

In the following embodiments of a video coding system, a video encoder20 and a video decoder 30 are described based on FIGS. 1 to 3.

FIG. 1A is a schematic block diagram illustrating an example codingsystem 10, e.g., a video coding system 10 (or short coding system 10)that may utilize techniques of this present application. Video encoder20 (or short encoder 20) and video decoder 30 (or short decoder 30) ofvideo coding system 10 represent examples of devices that may beconfigured to perform techniques in accordance with various examplesdescribed in the present application. As shown in FIG. 1A, the codingsystem 10 comprises a source device 12 configured to provide encodedpicture data 21 to a destination device 14 for decoding the encodedpicture data 13. The source device 12 comprises an encoder 20, and mayadditionally comprise a picture source 16, a pre-processor (orpre-processing unit) 18 such as a picture pre-processor, and acommunication interface or communication unit 22.

The picture source 16 may comprise or be any kind of picture capturingdevice, for example a camera for capturing a real-world picture, and/orany kind of a picture generating device, for example a computer-graphicsprocessor for generating a computer animated picture, or any kind ofother device for obtaining and/or providing a real-world picture, acomputer generated picture (e.g., a screen content, a virtual reality(VR) picture) and/or any combination thereof (e.g., an augmented reality(AR) picture). The picture source may be any kind of memory or storagestoring any of the aforementioned pictures.

In contrast to the pre-processor 18 and the processing performed by thepre-processing unit 18, the picture or picture data 17 may also bereferred to as raw picture or raw picture data. Pre-processor 18 isconfigured to receive the (raw) picture data 17 and to performpre-processing on the picture data 17 to obtain a pre-processed picture19 or pre-processed picture data 19. Pre-processing performed by thepre-processor 18 may, e.g., comprise trimming, color format conversion(e.g., from RGB to YCbCr), color correction, or de-noising. It might beunderstood that the pre-processing unit 18 may be optional component.The video encoder 20 is configured to receive the pre-processed picturedata 19 and to provide encoded picture data 21 (further details will bedescribed below, e.g., based on FIG. 2).

Communication interface 22 of the source device 12 may be configured toreceive the encoded picture data 21 and to transmit the encoded picturedata 21 (or any further processed version thereof) over communicationchannel 13 to another device, such as the destination device 14 or anyother device, for storage or reconstruction. The destination device 14comprises a decoder such as video decoder 30, and may additionallycomprise a communication interface or communication unit 28, apost-processor 32 (or post-processing unit 32) and a display device 34.The communication interface 28 of the destination device 14 isconfigured to receive the encoded picture data 21 (or any furtherprocessed version thereof) directly from the source device 12 or fromany other source, such as a storage device or an encoded picture datastorage device, and provide the encoded picture data 21 to the decoder30.

The communication interface 22 and the communication interface 28 may beconfigured to transmit or receive the encoded picture data 21 or encodeddata 13 via a direct communication link between the source device 12 andthe destination device 14, such as a direct wired or wirelessconnection, or via any kind of network, such as a wired or wirelessnetwork or any combination thereof, or any kind of private and publicnetwork, or any kind of combination thereof. The communication interface22 may be, e.g., configured to package the encoded picture data 21 intoan appropriate format such as packets, and/or process the encodedpicture data using any kind of transmission encoding or processing fortransmission over a communication link or communication network. Thecommunication interface 28, forming the counterpart of the communicationinterface 22, may be configured to receive the transmitted data andprocess the transmission data using any kind of correspondingtransmission decoding or processing and/or de-packaging to obtain theencoded picture data 21.

Communication interface 22 and communication interface 28 may beconfigured as unidirectional communication interfaces as indicated bythe arrow for the communication channel 13 in FIG. 1A pointing from thesource device 12 to the destination device 14, or bi-directionalcommunication interfaces, and may be configured to send and to receivemessages to, for example, set up a connection and to acknowledge andexchange any other information related to the communication link and/ordata transmission such as an encoded picture data transmission. Thedecoder 30 is configured to receive the encoded picture data 21 and toprovide decoded picture data 31 or a decoded picture 31 (further detailswill be described below with reference to FIG. 3 and FIG. 5).

The post-processor 32 of destination device 14 is configured topost-process the decoded picture data 31 (also called reconstructedpicture data) to obtain post-processed picture data such as apost-processed picture 33. The post-processing performed by thepost-processing unit 32 may comprise color format conversion (e.g. fromYCbCr to RGB), color correction, trimming, or re-sampling, or any otherprocessing for preparing the decoded picture data 31 for display, suchas by display device 34. The display device 34 of the destination device14 is configured to receive the post-processed picture data 33 fordisplaying the picture to a user or viewer. The display device 34 may beor comprise any kind of display for representing the reconstructedpicture, and can be in the form of an integrated or external display ormonitor. The displays may comprise liquid crystal displays (LCD),organic light emitting diodes (OLED) displays, plasma displays,projectors, micro LED displays, liquid crystal on silicon (LCoS),digital light processor (DLP) or any kind of other display.

Although FIG. 1A depicts the source device 12 and the destination device14 as separate devices, embodiments of devices may also comprisefunctionalities of both the source device 12 and the destination device14. In such embodiments the source device 12 or correspondingfunctionality and the destination device 14 may be implemented using thesame hardware and/or software or by separate hardware and/or software orany combination thereof. As will be apparent for the skilled personbased on the description, the existence and (specific) split offunctionalities of the different units or functionalities within thesource device 12 and/or destination device 14 as shown in FIG. 1A mayvary depending on the actual device and application.

One or both encoder 20 and decoder 30 may be implemented via processingcircuitry as shown in FIG. 1B, such as one or more microprocessors,digital signal processors (DSPs), application-specific integratedcircuits (ASICs), field-programmable gate arrays (FPGAs), discretelogic, hardware, video coding dedicated or any combinations thereof. Theencoder 20 may be implemented via processing circuitry 46 to embody thevarious modules as discussed with respect to encoder 20 of FIG. 2 and/orany other encoder system or subsystem described herein. The decoder 30may be implemented via processing circuitry 46 to embody the variousmodules as discussed with respect to decoder 30 of FIG. 3 and/or anyother decoder system or subsystem described herein. The processingcircuitry may be configured to perform the various operations asdiscussed later. As shown in FIG. 5, if the techniques are implementedpartially in software, a device may store instructions for the softwarein a suitable, non-transitory computer-readable storage medium and mayexecute the instructions in hardware using one or more processors toperform the techniques of this disclosure. Either of video encoder 20 orvideo decoder 30 may be integrated as part of a combined encoder/decoder(CODEC) in a single device, for example, as shown in FIG. 1B.

Source device 12 and destination device 14 may comprise any of a widerange of devices, including any kind of handheld or stationary devicessuch as notebook or laptop computers, mobile phones, smart phones,tablets or tablet computers, cameras, desktop computers, set-top boxes,televisions, display devices, digital media players, video gamingconsoles, video streaming devices (such as content services servers orcontent delivery servers), broadcast receiver device, broadcasttransmitter device, or the like and may use any kind of operatingsystem. In some cases, the source device 12 and the destination device14 may be equipped for wireless communication. Thus, the source device12 and the destination device 14 may be wireless communication devices.

In some cases, video coding system 10 illustrated in FIG. 1A is merelyan example and the techniques of the present application may apply tovideo coding settings (e.g., video encoding or video decoding) that donot necessarily include any data communication between the encoding anddecoding devices. In other examples, data is retrieved from a localmemory and streamed over a network or the like. A video encoding devicemay encode and store data to memory, and/or a video decoding device mayretrieve and decode data from memory. In some examples, the encoding anddecoding is performed by devices that do not communicate with oneanother, but simply encode data to memory and/or retrieve and decodedata from memory. For convenience of description, embodiments of theapplication are described herein, for example, by reference toHigh-Efficiency Video Coding (HEVC) or to the reference software ofVersatile Video coding (VVC), the next generation video coding standarddeveloped by the Joint Collaboration Team on Video Coding (JCT-VC) ofITU-T Video Coding Experts Group (VCEG) and ISO/IEC Motion PictureExperts Group (MPEG). One of ordinary skill in the art will understandthat embodiments of the application are not limited to HEVC or VVC.

Encoder and Encoding Method

FIG. 2 shows a schematic block diagram of an example video encoder 20that is configured to implement the techniques of an embodiment of thepresent disclosure. In the example of FIG. 2, the video encoder 20comprises an input 201 (or input interface 201), a residual calculationunit 204, a transform processing unit 206, a quantization unit 208, aninverse quantization unit 210, and inverse transform processing unit212, a reconstruction unit 214, a loop filter unit 220, a decodedpicture buffer (DPB) 230, a mode selection unit 260, an entropy encodingunit 270 and an output 272 (or output interface 272). The mode selectionunit 260 may include an inter-prediction unit 244, an intra-predictionunit 254 and a partitioning unit 262. Inter-prediction unit 244 mayinclude a motion estimation unit and a motion compensation unit (notshown). A video encoder 20 as shown in FIG. 2 may also be referred to ashybrid video encoder or a video encoder according to a hybrid videocodec. The residual calculation unit 204, the transform processing unit206, the quantization unit 208, and the mode selection unit 260 may bereferred to as forming a forward signal path of the encoder 20, whereasthe inverse quantization unit 210, the inverse transform processing unit212, the reconstruction unit 214, the buffer 216, the loop filter 220,the decoded picture buffer (DPB) 230, the inter-prediction unit 244 andthe intra-prediction unit 254 may be referred to as forming a backwardsignal path of the video encoder 20, wherein the backward signal path ofthe video encoder 20 corresponds to the signal path of the decoder (seevideo decoder 30 in FIG. 3). The inverse quantization unit 210, theinverse transform processing unit 212, the reconstruction unit 214, theloop filter 220, the decoded picture buffer (DPB) 230, theinter-prediction unit 244 and the intra-prediction unit 254 are alsoreferred to forming the “built-in decoder” of video encoder 20.

Pictures & Picture Partitioning (Pictures & Blocks)

The encoder 20 may be configured to receive via input 201, a picture 17(or picture data) such as a picture of a sequence of pictures forming avideo or video sequence. The received picture or picture data may alsobe in the form of a pre-processed picture 19 (or pre-processed picturedata). For sake of simplicity the following description refers to thepicture 17. The picture 17 may also be referred to as “current” pictureor picture to be coded (in particular in video coding to distinguish thecurrent picture from other pictures such as those previously encodedand/or decoded pictures of the same video sequence, i.e., the videosequence which also comprises the current picture).

A (digital) picture is or might be regarded as a two-dimensional arrayor matrix of samples with intensity values. A sample in the array mayalso be referred to as pixel (short form of picture element) or a “pel”.The number of samples in horizontal and vertical direction (or axis) ofthe array or picture define the size and/or resolution of the picture.For representation of color, typically three color components areemployed, i.e., the picture may be represented or include three samplearrays. In RBG format or color space a picture comprises a correspondingred, green and blue sample array. However, in video coding each pixel istypically represented in a luminance and chrominance format or colorspace, e.g., YCbCr, which comprises a luminance component indicated by Y(sometimes also L is used instead) and two chrominance componentsindicated by Cb and Cr. The luminance (or “luma”) component Y representsthe brightness or grey level intensity (e.g., like in a grey-scalepicture), while the two chrominance (or “chroma”) components Cb and Crrepresent the chromaticity or color information components.

Accordingly, a picture in YCbCr format comprises a luminance samplearray of luminance sample values (Y), and two chrominance sample arraysof chrominance values (Cb and Cr). Pictures in RGB format may beconverted or transformed into YCbCr format and vice versa, the processis also known as color transformation or conversion. If a picture ismonochrome, the picture may comprise only a luminance sample array.Accordingly, a picture may be, for example, an array of luma samples inmonochrome format or an array of luma samples and two correspondingarrays of chroma samples in 4:2:0, 4:2:2, and 4:4:4 color format.

Embodiments of the video encoder 20 may comprise a picture partitioningunit (not depicted in FIG. 2) configured to partition the picture 17into a plurality of (typically non-overlapping) picture blocks 203.These blocks may also be referred to as root blocks, macro blocks(H.264/AVC) or coding tree blocks (CTB) or coding tree units (CTU)(H.265/HEVC and VVC). The picture partitioning unit may be configured touse the same block size for all pictures of a video sequence and thecorresponding grid defining the block size, or to change the block sizebetween pictures or subsets or groups of pictures, and partition eachpicture into the corresponding blocks.

In further embodiments, the video encoder may be configured to receivedirectly a block 203 of the picture 17, e.g., one, several or all blocksforming the picture 17. The picture block 203 may also be referred to ascurrent picture block or picture block to be coded.

Like the picture 17, the picture block 203 again is or might be regardedas a two-dimensional array or matrix of samples with intensity values(sample values), although of smaller dimension than the picture 17. Inother words, the block 203 may comprise one sample array (e.g., a lumaarray in case of a monochrome picture 17, or a luma or chroma array incase of a color picture) or three sample arrays (e.g., a luma and twochroma arrays in case of a color picture 17) or any other number and/orkind of arrays depending on the color format applied. The number ofsamples in horizontal and vertical direction (or axis) of the block 203define the size of block 203. Accordingly, a block may, for example, bein the form of an M×N (M-column by N-row) array of samples, or an M×Narray of transform coefficients.

Embodiments of the video encoder 20 as shown in FIG. 2 may be configuredto encode the picture 17 block by block such that the encoding andprediction is performed per block 203. Embodiments of the video encoder20 as shown in FIG. 2 may be further configured to partition and/orencode the picture by using slices (also referred to as video slices),for which a picture may be partitioned into or encoded using one or moreslices (typically non-overlapping), and each slice may comprise one ormore blocks (such as CTUs) or one or more groups of blocks (such astiles (H.265/HEVC and VVC) or bricks (VVC)).

Embodiments of the video encoder 20 as shown in FIG. 2 may be furtherconfigured to partition and/or encode the picture by using slices/tilegroups (also referred to as video tile groups) and/or tiles (alsoreferred to as video tiles), wherein a picture may be partitioned intoor encoded using one or more slices/tile groups (typicallynon-overlapping), and each slice/tile group may comprise one or moreblocks (CTUs) or one or more tiles, for which each tile may be ofrectangular shape and may comprise one or more complete or fractionalblocks (CTUs).

Residual Calculation

The residual calculation unit 204 may be configured to calculate aresidual block 205 (also referred to as “residual”) based on the pictureblock 203 and a prediction block 265 such as by subtracting samplevalues of the prediction block 265 from sample values of the pictureblock 203, sample by sample (pixel by pixel) to obtain the residualblock 205 in the sample domain. Further details about the predictionblock 265 are provided below.

Transform

The transform processing unit 206 may be configured to apply atransform, such as a discrete cosine transform (DCT) or discrete sinetransform (DST), on the sample values of the residual block 205 toobtain transform coefficients 207 in a transform domain. The transformcoefficients 207 may also be referred to as “transform residualcoefficients” and represent the residual block 205 in the transformdomain. The transform processing unit 206 may be configured to applyinteger approximations of DCT/DST, such as the transforms specified forH.265/HEVC. Compared to an orthogonal DCT transform, such integerapproximations are typically scaled by a certain factor. In order topreserve the norm of the residual block which is processed by forwardand inverse transforms, additional scaling factors are applied as partof the transform process. The scaling factors are typically chosen basedon certain constraints like scaling factors being a power of two forshift operations, bit depth of the transform coefficients, tradeoffbetween accuracy and implementation costs, and the like. Specificscaling factors may, for example, be specified for the inversetransform, such as by inverse transform processing unit 212 (and thecorresponding inverse transform (such as by inverse transform processingunit 312 at video decoder 30) and corresponding scaling factors for theforward transform, e.g., by transform processing unit 206, at an encoder20. Embodiments of the video encoder 20 (respectively transformprocessing unit 206) may be configured to output transform parameterssuch as type of transform or transforms, such as whether the transformsare directly or encoded or compressed via the entropy encoding unit 270,so that the video decoder 30 may receive and use the transformparameters for decoding.

Quantization

The quantization unit 208 may be configured to quantize the transformcoefficients 207 to obtain quantized coefficients 209 by, for example,applying scalar quantization or vector quantization. The quantizedcoefficients 209 may also be referred to as “quantized transformcoefficients” 209 or “quantized residual coefficients” 209. Thequantization process may reduce the bit depth associated with some orall of the transform coefficients 207. For example, an n-bit transformcoefficient may be rounded down to an m-bit Transform coefficient duringquantization, where n is greater than m. The degree of quantization maybe modified by adjusting a quantization parameter (QP). For example, forscalar quantization, different scaling may be applied to achieve fineror coarser quantization. Smaller quantization step sizes correspond tofiner quantization, whereas larger quantization step sizes correspond tocoarser quantization. The applicable quantization step size may beindicated by a quantization parameter (QP). The quantization parametermay for example be an index to a predefined set of applicablequantization step sizes. For example, small quantization parameters maycorrespond to fine quantization (small quantization step sizes) andlarge quantization parameters may correspond to coarse quantization(large quantization step sizes) or vice versa. The quantization mayinclude division by a quantization step size and a corresponding inversedequantization (such as by inverse quantization unit 210) and mayinclude multiplication by the quantization step size. Embodimentsaccording to some standards (for example, HEVC) may be configured to usea quantization parameter to determine the quantization step size.Generally, the quantization step size may be calculated based on aquantization parameter using a fixed-point approximation of an equationincluding division. Additional scaling factors may be introduced forquantization and dequantization to restore the norm of the residualblock, which might get modified because of the scaling used in thefixed-point approximation of the equation for quantization step size andquantization parameter. In one example implementation, the scaling ofthe inverse transform and dequantization might be combined.Alternatively, customized quantization tables may be used and signaledfrom an encoder to a decoder, such as in a bitstream. The quantizationis a lossy operation, for which the loss increases with increasingquantization step sizes. Embodiments of the video encoder 20(respectively quantization unit 208) may be configured to outputquantization parameters (“QP”) directly or encoded via the entropyencoding unit 270 so that, for example, the video decoder 30 may receiveand apply the quantization parameters for decoding.

Inverse Quantization

The inverse quantization unit 210 is configured to apply the inversequantization of the quantization unit 208 on the quantized coefficientsto obtain dequantized coefficients 211 such as by applying the inverseof the quantization scheme applied by the quantization unit 208 based onor using the same quantization step size as the quantization unit 208.The dequantized coefficients 211 may also be referred to as “dequantizedresidual coefficients” 211 and correspond—although typically notidentical to the transform coefficients due to the loss byquantization—to the transform coefficients 207.

Inverse Transform

The inverse transform processing unit 212 is configured to apply theinverse transform of the transform applied by the transform processingunit 206 (that is, apply an inverse discrete cosine transform (DCT) orinverse discrete sine transform (DST) or other inverse transforms) toobtain a reconstructed residual block 213 (or corresponding dequantizedcoefficients 213) in the sample domain. The reconstructed residual block213 may also be referred to as a “transform block”.

Reconstruction

The reconstruction unit 214 (e.g., adder or summer 214) is configured toadd the transform block 213 (i.e., reconstructed residual block) to theprediction block 265 to obtain a reconstructed block 215 in the sampledomain, such as by adding—sample by sample—the sample values of thereconstructed residual block 213 and the sample values of the predictionblock 265.

Filtering

The loop filter unit 220 is configured to filter the reconstructed block215 to obtain a filtered block 221, or in general, to filterreconstructed samples to obtain filtered sample values. The loop filterunit is configured to smooth pixel transitions, or otherwise improve thevideo quality. The loop filter unit 220 may comprise one or more loopfilters such as a de-blocking filter, a sample-adaptive offset (SAO)filter or one or more other filters (such as an adaptive loop filter(ALF), a noise suppression filter (NSF)), or any combination ofde-blocking filter, SAO filter, ALF filter, or NSF filter. In anexample, the loop filter unit 220 may comprise a de-blocking filter, aSAO filter and an ALF filter. The order of the filtering process may bethe deblocking filter, SAO and ALF. In another example, a process calledthe luma mapping with chroma scaling (LMCS) (namely, the adaptivein-loop re-shaper) is added. This process is performed beforedeblocking. In another example, the deblocking filter process may bealso applied to internal sub-block edges, such as affine sub-blocksedges, advanced temporal motion vector prediction (ATMVP) sub-blocksedges, sub-block transform (SBT) edges and intra sub-partition (ISP)edges. Although the loop filter unit 220 is shown in FIG. 2 as being anin-loop filter, in other configurations, the loop filter unit 220 may beimplemented as a post-loop filter. The filtered block 221 may also bereferred to as a filtered reconstructed block 221. Embodiments of thevideo encoder 20 (respectively loop filter unit 220) may be configuredto output loop filter parameters (such as SAO filter parameters or ALFfilter parameters or LMCS parameters) directly or encoded via theentropy encoding unit 270, so that a decoder 30 may receive and applythe same loop filter parameters or respective loop filters for decoding.

Decoded Picture Buffer

The decoded picture buffer (DPB) 230 may be a memory that storesreference pictures, or in general reference picture data, for encodingvideo data by video encoder 20. The DPB 230 may be formed by any of avariety of memory devices, such as dynamic random access memory (DRAM),including synchronous DRAM (SDRAM), magneto-resistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. The decodedpicture buffer (DPB) 230 may be configured to store one or more filteredblocks 221. The decoded picture buffer 230 may be further configured tostore other previously filtered blocks, such as previously reconstructedand filtered blocks 221, of the same current picture or of different(e.g., previously reconstructed) pictures, and may provide complete,previously reconstructed (i.e., decoded), pictures and correspondingreference blocks and samples and/or a partially reconstructed currentpicture (and corresponding reference blocks and samples), for examplefor inter-prediction. The decoded picture buffer (DPB) 230 may also beconfigured to store one or more unfiltered reconstructed blocks 215, orin general unfiltered reconstructed samples, e.g., if the reconstructedblock 215 is not filtered by loop filter unit 220, or any other furtherprocessed version of the reconstructed blocks or samples.

Mode Selection (Partitioning & Prediction)

The mode selection unit 260 comprises partitioning unit 262,inter-prediction unit 244 and intra-prediction unit 254, and isconfigured to receive or obtain original picture data such as anoriginal block 203 (current block 203 of the current picture 17), andreconstructed picture data such as filtered and/or unfilteredreconstructed samples or blocks of the same (current) picture and/orfrom one or a plurality of previously decoded pictures from decodedpicture buffer 230 or other buffers such as line buffers (not shown).The reconstructed picture data is used as reference picture data forprediction, inter-prediction or intra-prediction, to obtain a predictionblock 265 or predictor 265. Mode selection unit 260 may be configured todetermine or select a partitioning for a current block prediction mode(including no partitioning) and a prediction mode (such as an intra orinter-prediction mode) and generate a corresponding prediction block 265that can be used for the calculation of the residual block 205 and forthe reconstruction of the reconstructed block 215.

Embodiments of the mode selection unit 260 may be configured to selectthe partitioning and the prediction mode from the modes supported by oravailable for mode selection unit 260) that provides the best match orthe minimum residual (“minimum residual” means better compression fortransmission or storage), or a minimum signaling overhead (“minimumsignaling overhead” means better compression for transmission orstorage), or which considers or balances both. The mode selection unit260 may be configured to determine the partitioning and prediction modebased on rate distortion optimization (RDO), i.e., select the predictionmode which provides a minimum rate distortion. Terms like “best”,“minimum”, “optimum” etc. in this context do not necessarily refer to anoverall “best”, “minimum”, “optimum”, etc. but may also refer to thefulfillment of a termination or selection criterion like a valueexceeding or falling below a threshold or other constraints leadingpotentially to a “sub-optimum selection” but reducing complexity andprocessing time. In other words, the partitioning unit 262 may beconfigured to partition a picture from a video sequence into a sequenceof coding tree units (CTUs), and the CTU 203 may be further partitionedinto smaller block partitions or sub-blocks (which form again blocks)iteratively using quad-tree-partitioning (QT), binary partitioning (BT),triple-tree-partitioning (TT), or any combination thereof, and toperform the prediction for each of the block partitions or sub-blocks,wherein the mode selection comprises the selection of the tree-structureof the partitioned block 203 and the prediction modes are applied toeach of the block partitions or sub-blocks. Partitioning by partitioningunit 260 and prediction processing inter-prediction unit 244 andintra-prediction unit 254 performed by an example video encoder 20 isexplained in greater detail below.

Partitioning

The partitioning unit 262 may be configured to partition a picture froma video sequence into a sequence of coding tree units (CTUs), and thepartitioning unit 262 may partition (or split) a coding tree unit (CTU)203 into smaller partitions or smaller blocks of square or rectangularshape. For a picture that has three sample arrays, a CTU consists of anN×N block of luma samples together with two corresponding blocks ofchroma samples. The maximum allowed size of the luma block in a CTU isspecified to be 128×128 in the developing versatile video coding (VVC),but it might be specified to be value rather than 128×128 in the future,for example, 256×256. The CTUs of a picture may be clustered/grouped asslices/tile groups, tiles or bricks. A tile covers a rectangular regionof a picture, and a tile might be divided into one or more bricks. Abrick consists of a number of CTU rows within a tile. A tile that is notpartitioned into multiple bricks might be referred to as a brick.However, a brick is a true subset of a tile and is not referred to as atile. There are two modes of tile groups supported in VVC, namely theraster-scan slice/tile group mode and the rectangular slice mode. In theraster-scan tile group mode, a slice/tile group contains a sequence oftiles in tile raster scan of a picture. In the rectangular slice mode, aslice contains a number of bricks of a picture that collectively form arectangular region of the picture. The bricks within a rectangular sliceare in the order of brick raster scan of the slice. These smaller blocks(which may also be referred to as sub-blocks) may be further partitionedinto even smaller partitions. This is also referred to tree-partitioningor hierarchical tree-partitioning, wherein a root block (for example, ablock at root tree-level 0 (hierarchy-level 0, depth 0), may berecursively partitioned into two or more blocks of a next lowertree-level (e.g., nodes at tree-level 1 (hierarchy-level 1, depth 1)),wherein these blocks may be again partitioned into two or more blocks ofa next lower level (e.g., tree-level 2 (hierarchy-level 2, depth 2)),etc. until the partitioning is terminated, a when because a terminationcriterion is fulfilled, as when a maximum tree depth or minimum blocksize is reached. Blocks which are not further partitioned are alsoreferred to as leaf-blocks or leaf nodes of the tree. A tree usingpartitioning into two partitions is referred to as binary-tree (BT), atree using partitioning into three partitions is referred to asternary-tree (TT), and a tree using partitioning into four partitions isreferred to as quad-tree (QT). For example, a coding tree unit (CTU) maybe or comprise a coding tree block (CTB) of luma samples, twocorresponding CTBs of chroma samples of a picture that has three samplearrays, or a CTB of samples of a monochrome picture or a picture that iscoded using three separate color planes and syntax structures used tocode the samples. Correspondingly, a CTB may be an N×N block of samplesfor some value of N such that the division of a component into CTBs is apartitioning. A coding unit (CU) may be or comprise a coding block ofluma samples, two corresponding coding blocks of chroma samples of apicture that has three sample arrays, or a coding block of samples of amonochrome picture or a picture that is coded using three separate colorplanes and syntax structures used to code the samples. A coding block(CB) may be an M×N block of samples for some values of M and N such thatthe division of a CTB into coding blocks is a partitioning.

In HEVC embodiments, a coding tree unit (CTU) may be split into a numberof coding units (CUs) by using a quad-tree structure denoted as a codingtree. The decision whether to code a picture area using inter-picture(temporal) or intra-picture (spatial) prediction is made at the leaf CUlevel. Each leaf CU might be further split into one, two or fourPrediction Unit (PU) according to the PU splitting type. Inside one PU,the same prediction process is applied, and the relevant information istransmitted to the decoder on a PU basis. After obtaining the residualblock by applying the prediction process based on the PU splitting type,a leaf CU might be partitioned into transform units (TUs) according toanother quadtree structure similar to the coding tree for the CU. Inembodiments according to the Versatile Video Coding (VVC) standard, acombined Quad-tree nested multi-type tree using binary and ternarysplits segmentation structure to partition a coding tree unit. In thecoding tree structure within a coding tree unit, a CU can have either asquare or rectangular shape. For example, the coding tree unit (CTU) isfirst partitioned by a quaternary tree. The quaternary tree leaf nodesmight be further partitioned by a multi-type tree structure. There arefour splitting types in multi-type tree structure: vertical binarysplitting (SPLIT_BT_VER), horizontal binary splitting (SPLIT_BT_HOR),vertical ternary splitting (SPLIT_TT_VER), and horizontal ternarysplitting (SPLIT_TT_HOR). The multi-type tree leaf nodes are calledcoding units (CUs), and unless the CU is too large for the maximumtransform length, this segmentation is used for prediction and transformprocessing without any further partitioning. This means that, in mostcases, the CU, PU and TU have the same block size in the quad-tree withnested multi-type tree coding block structure. The exception occurs whenmaximum supported transform length is smaller than the width or heightof the color component of the CU.

VVC develops a unique signaling mechanism of the partition splittinginformation in quad-tree with nested multi-type tree coding treestructure. In the signaling mechanism, a coding tree unit (CTU) istreated as the root of a quaternary tree and is first partitioned by aquaternary tree structure. Each quaternary tree leaf node (whensufficiently large to allow it) is then further partitioned by amulti-type tree structure. In the multi-type tree structure, a firstflag (mtt_split_cu_flag) is signaled to indicate whether the node isfurther partitioned; when a node is further partitioned, a second flag(mtt_split_cu_vertical_flag) is signaled to indicate the splittingdirection, and then a third flag (mtt_split_cu_binary_flag) is signaledto indicate whether the split is a binary split or a ternary split.Based on the values of mtt_split_cu_vertical_flag andmtt_split_cu_binary_flag, the multi-type tree slitting mode(MttSplitMode) of a CU might be derived by a decoder based on apredefined rule or a table. It should be noted, for a certain design,for example, 64×64 Luma block and 32×32 Chroma pipelining design in VVChardware decoders, TT split is forbidden when either width or height ofa luma coding block is larger than 64, as shown in FIG. 6. TT split isalso forbidden when either width or height of a chroma coding block islarger than 32. The pipelining design will divide a picture into Virtualpipeline data units (VPDUs) which are defined as non-overlapping unitsin a picture. In hardware decoders, successive VPDUs are processed bymultiple pipeline stages simultaneously. The VPDU size is roughlyproportional to the buffer size in most pipeline stages, so it isimportant to keep the VPDU size small. In most hardware decoders, theVPDU size might be set to maximum transform block (TB) size. However, inVVC, ternary tree (TT) and binary tree (BT) partition may lead to theincreasing of VPDUs sizes. In addition, it should be noted that, when aportion of a tree node block exceeds the bottom or right pictureboundary, the tree node block is forced to be split until all samples ofevery coded CU are located inside the picture boundaries.

As an example, the Intra Sub-Partitions (ISP) tool may divide lumaintra-predicted blocks vertically or horizontally into 2 or 4sub-partitions depending on the block size.

In one example, the mode selection unit 260 of video encoder 20 may beconfigured to perform any combination of the partitioning techniquesdescribed herein. As described above, the video encoder 20 is configuredto determine or select the best or an optimum prediction mode from a setof pre-determined prediction modes. The set of prediction modes maycomprise intra-prediction modes and/or inter-prediction modes.

Intra-Prediction

The set of intra-prediction modes may comprise 35 differentintra-prediction modes, such as non-directional modes, like DC (or mean)mode and planar mode, or directional modes, such as defined in HEVC, ormay comprise 67 different intra-prediction modes (e.g., non-directionalmodes like DC (or mean) mode and planar mode), or directional modes suchas those defined for VVC. As an example, several conventional angularintra prediction modes are adaptively replaced with wide-angle intraprediction modes for the non-square blocks such as those defined forVVC. As another example, to avoid division operations for DC prediction,only the longer side is used to compute the average for non-squareblocks. Results of intra-rediction of planar mode may be furthermodified by a position dependent intra-prediction combination (PDPC)method.

The intra-prediction unit 254 is configured to use reconstructed samplesof neighboring blocks of the same current picture to generate anintra-prediction block 265 according to an intra-prediction mode of theset of intra-prediction modes.

The intra-prediction unit 254 (or in general, the mode selection unit260) is further configured to output intra-prediction parameters (or ingeneral, information indicative of the selected intra prediction modefor the block) to the entropy encoding unit 270 in form of syntaxelements 266 for inclusion into the encoded picture data 21 so that thevideo decoder 30 may receive and use the prediction parameters fordecoding.

Inter-Prediction

The set of (or possible) inter-prediction modes depends on the availablereference pictures (i.e., previous at least partially decoded picturessuch as pictures stored in DBP 230) and other inter-predictionparameters such as those that determine whether the whole referencepicture or only a part, such as a search window area around the area ofthe current block, of the reference picture is used for searching for abest matching reference block, and/or whether pixel interpolation isapplied, half/semi-pel, quarter-pel and/or 1/16 pel interpolation, ornot.

Additional to the above prediction modes, skip mode, direct mode and/orother inter-prediction mode may be applied. For example, for extendedmerge prediction, the merge candidate list of such mode is constructedby including the following five types of candidates in order: Spatialmotion vector prediction (MVP) from spatial neighbor CUs, Temporal MVPfrom collocated CUs, History-based MVP from a first in-first out (FIFO)table, Pairwise average MVP and Zero MVs. A bilateral-matching baseddecoder side motion vector refinement (DMVR) may be applied to increasethe accuracy of the MVs of the merge mode. Merge mode with motion vectordifference, MVD (MMVD), which comes from merge mode with motion vectordifferences. A MMVD flag is signaled right after sending a skip flag andmerge flag to specify whether MMVD mode is used for a CU. And a CU-leveladaptive motion vector resolution (AMVR) scheme may be applied. AMVRallows MVD of the CU to be coded in different precision. Dependent onthe prediction mode for the current CU, the MVDs of the current CU mightbe adaptively selected. When a CU is coded in merge mode, the combinedinter/intra prediction (CIIP) mode may be applied to the current CU.Weighted averaging of the inter and intra prediction signals isperformed to obtain the CIIP prediction. Affine motion compensatedprediction, the affine motion field of the block is described by motioninformation of two control point (4-parameter) or three control pointmotion vectors (6-parameter). Subblock-based temporal motion vectorprediction (SbTMVP), which is similar to the temporal motion vectorprediction (TMVP) in HEVC, but predicts the motion vectors of thesub-CUs within the current CU. Bi-directional optical flow (BDOF),previously referred to as BIO, is a simpler version that requires muchless computation, especially in terms of number of multiplications andthe size of the multiplier.

The inter-prediction unit 244 may include a motion estimation (ME) unitand a motion compensation (MC) unit (both not shown in FIG. 2). Themotion estimation unit may be configured to receive or obtain thepicture block 203 (current picture block 203 of the current picture 17)and a decoded picture 231, or at least one or a plurality of previouslyreconstructed blocks such as reconstructed blocks of one or a pluralityof other/different previously decoded pictures 231, for motionestimation. The picture block 203 may be in the form of a video sequencemay comprise the current picture and the previously decoded pictures231, or in other words, the current picture and the previously decodedpictures 231 may be part of or form a sequence of pictures forming avideo sequence. The encoder 20 may be configured to select a referenceblock from a plurality of reference blocks of the same or differentpictures of the plurality of other pictures and provide a referencepicture (or reference picture index) and/or an offset (spatial offset)between the position (x, y coordinates) of the reference block and theposition of the current block as inter-prediction parameters to themotion estimation unit. This offset is also called motion vector (MV).

The motion compensation unit is configured to obtain or to receive, aninter-prediction parameter and to perform inter-prediction based on orusing the inter-prediction parameter to obtain an inter-prediction block265. Motion compensation, performed by the motion compensation unit, mayinvolve fetching or generating the prediction block based on themotion/block vector determined by motion estimation, possibly performinginterpolations to sub-pixel precision. Interpolation filtering maygenerate additional pixel samples from known pixel samples, thuspotentially increasing the number of candidate prediction blocks thatmay be used to code a picture block. Upon receiving the motion vectorfor the PU of the current picture block, the motion compensation unitmay locate the prediction block to which the motion vector points in oneof the reference picture lists. The motion compensation unit may alsogenerate syntax elements associated with the blocks and video slices foruse by video decoder 30 in decoding the picture blocks of the videoslice. In addition or as an alternative to slices and respective syntaxelements, tile groups and/or tiles and respective syntax elements may begenerated or used.

Entropy Coding

The entropy encoding unit 270 is configured to apply, for example, anentropy encoding algorithm or scheme (e.g., a variable length coding(VLC) scheme, an context adaptive VLC scheme (CAVLC), an arithmeticcoding scheme, a binarization, a context adaptive binary arithmeticcoding (CABAC), syntax-based context-adaptive binary arithmetic coding(SBAC), probability interval partitioning entropy (PIPE) coding oranother entropy encoding methodology or technique) or bypass (nocompression) on the quantized coefficients 209, inter-predictionparameters, intra prediction parameters, loop filter parameters and/orother syntax elements) to obtain encoded picture data 21 which can beoutput via the output 272 such as in the form of an encoded bitstream 21so that the video decoder 30 may receive and use the parameters fordecoding. The encoded bitstream 21 may be transmitted to video decoder30, or stored in a memory for later transmission or retrieval by videodecoder 30. Other structural variations of the video encoder 20 might beused to encode the video stream. For example, a non-transform basedencoder 20 can quantize the residual signal directly without thetransform processing unit 206 for certain blocks or frames. In anotherimplementation, an encoder 20 can have the quantization unit 208 and theinverse quantization unit 210 combined into a single unit.

Decoder and Decoding Method

FIG. 3 shows an example of a video decoder 30 that is configured toimplement the techniques of this present application. The video decoder30 is configured to receive encoded picture data 21 (e.g., encodedbitstream) encoded by encoder 20 to obtain a decoded picture 331. Theencoded picture data or bitstream comprises information for decoding theencoded picture data, such as data that represents picture blocks of anencoded video slice (and/or tile groups or tiles) and associated syntaxelements. In the example of FIG. 3, the decoder 30 comprises an entropydecoding unit 304, an inverse quantization unit 310, an inversetransform processing unit 312, a reconstruction unit 314 (such as asummer), a loop filter 320, a decoded picture buffer (DBP) 330, a modeapplication unit 360, an inter-prediction unit 344 and an intraprediction unit 354. Inter-prediction unit 344 may be or include amotion compensation unit. Video decoder 30 may, in some examples,perform a decoding pass generally reciprocal to the encoding passdescribed with respect to video encoder 100 from FIG. 2.

As explained with regard to the encoder 20, the inverse quantizationunit 210, the inverse transform processing unit 212, the reconstructionunit 214, the loop filter 220, the decoded picture buffer (DPB) 230, theinter-prediction unit 344 and the intra prediction unit 354 are alsoreferred to as forming the “built-in decoder” of video encoder 20.Accordingly, the inverse quantization unit 310 may be identical infunction to the inverse quantization unit 110, the inverse transformprocessing unit 312 may be identical in function to the inversetransform processing unit 212, the reconstruction unit 314 may beidentical in function to reconstruction unit 214, the loop filter 320may be identical in function to the loop filter 220, and the decodedpicture buffer 330 may be identical in function to the decoded picturebuffer 230. Therefore, the explanations provided for the respectiveunits and functions of the video 20 encoder apply correspondingly to therespective units and functions of the video decoder 30.

Entropy Decoding

The entropy decoding unit 304 is configured to parse the bitstream 21(or in general encoded picture data 21) and perform, for example,entropy decoding to the encoded picture data 21 to obtain quantizedcoefficients 309 and/or decoded coding parameters (not shown in FIG. 3),any or all of inter-prediction parameters (such as reference pictureindex and motion vector), intra prediction parameter (such asintra-prediction mode or index), transform parameters, quantizationparameters, loop filter parameters, and/or other syntax elements.Entropy decoding unit 304 may be configured to apply the decodingalgorithms or schemes corresponding to the encoding schemes as describedwith regard to the entropy encoding unit 270 of the encoder 20.

Entropy decoding unit 304 may be further configured to provideinter-prediction parameters, intra prediction parameter and/or othersyntax elements to the mode application unit 360 and other parameters toother units of the decoder 30. Video decoder 30 may receive the syntaxelements at the video slice level and/or the video block level. Inaddition or as an alternative to slices and respective syntax elements,tile groups and/or tiles and respective syntax elements may be receivedand/or used.

Inverse Quantization

The inverse quantization unit 310 may be configured to receivequantization parameters (QP) (or in general information related to theinverse quantization) and quantized coefficients from the encodedpicture data 21 (which can be obtained by parsing and/or decoding byentropy decoding unit 304) and to apply, based on the quantizationparameters, an inverse quantization on the decoded quantizedcoefficients 309 to obtain dequantized coefficients 311 (also referredto as transform coefficients. The inverse quantization process mayinclude use of a quantization parameter determined by video encoder 20for each video block in the video slice (or tile or tile group) todetermine a degree of quantization and, likewise, a degree of inversequantization that should be applied.

Inverse Transform

Inverse transform processing unit 312 may be configured to receivedequantized coefficients 311, also referred to as transformcoefficients, and to apply a transform to the dequantized coefficients311 in order to obtain reconstructed residual blocks 213 in the sampledomain. The reconstructed residual blocks 213 may also be referred to astransform blocks. The transform may be an inverse transform, such as aninverse DCT, an inverse DST, an inverse integer transform, or aconceptually similar inverse transform process. The inverse transformprocessing unit 312 may be further configured to receive transformparameters or corresponding information from the encoded picture data 21(such as by parsing and/or decoding by entropy decoding unit 304) todetermine the transform to be applied to the dequantized coefficients311.

Reconstruction

The reconstruction unit 314 (adder or summer) may be configured to addthe reconstructed residual block 313 to the prediction block 365 toobtain a reconstructed block 315 in the sample domain, such as by addingthe sample values of the reconstructed residual block 313 and the samplevalues of the prediction block 365.

Filtering

The loop filter unit 320 (either in the coding loop or after the codingloop) is configured to filter the reconstructed block 315 to obtain afiltered block 321 to smooth pixel transitions, or otherwise improve thevideo quality. The loop filter unit 320 may comprise one or more loopfilters such as a de-blocking filter, a sample-adaptive offset (SAO)filter or one or more other filters, such as an adaptive loop filter(ALF), a noise suppression filter (NSF), or any combination thereof. Inan example, the loop filter unit 220 may comprise a de-blocking filter,a SAO filter and an ALF filter. The order of the filtering process maybe the deblocking filter, SAO and ALF. In another example, a processcalled the luma mapping with chroma scaling (LMCS) (namely, the adaptivein-loop reshaper) is added. This process is performed beforede-blocking. In another example, the de-blocking filter process may bealso applied to internal sub-block edges, such as affine sub-blocksedges, ATMVP sub-blocks edges, sub-block transform (SBT) edges and intrasub-partition (ISP) edges. Although the loop filter unit 320 is shown inFIG. 3 as being an in-loop filter, in other configurations, the loopfilter unit 320 may be implemented as a post-loop filter.

Decoded Picture Buffer

The decoded video blocks 321 of a picture are then stored in decodedpicture buffer 330, which stores the decoded pictures 331 as referencepictures for subsequent motion compensation for other pictures and/orfor output respectively display. The decoder 30 is configured to outputthe decoded picture 311 via output 312 for presentation or viewing to auser.

Prediction

The inter-prediction unit 344 may be identical to the inter-predictionunit 244 (in particular, to the motion compensation unit) and theintra-prediction unit 354 may be identical to the inter-prediction unit254 in function, and performs split or partitioning decisions andprediction based on the partitioning and/or prediction parameters orrespective information received from the encoded picture data 21 (suchas by parsing and/or decoding by entropy decoding unit 304). Modeapplication unit 360 may be configured to perform the prediction (intra-or inter-prediction) per block based on reconstructed pictures, blocksor respective samples (filtered or unfiltered) to obtain the predictionblock 365. When the video slice is coded as an intra-coded (I) slice,intra-prediction unit 354 of mode application unit 360 is configured togenerate prediction block 365 for a picture block of the current videoslice based on a signaled intra-prediction mode and data from previouslydecoded blocks of the current picture. When the video picture is codedas an inter-coded (i.e., B, or P) slice, inter-prediction unit 344(e.g., motion compensation unit) of mode application unit 360 isconfigured to produce prediction blocks 365 for a video block of thecurrent video slice based on the motion vectors and other syntaxelements received from entropy decoding unit 304. For inter-prediction,the prediction blocks may be produced from one of the reference pictureswithin one of the reference picture lists. Video decoder 30 mayconstruct the reference frame lists, List 0 and List 1, using defaultconstruction techniques based on reference pictures stored in DPB 330.The same or similar may be applied for or by embodiments using tilegroups such as video tile groups and/or tiles such as video tiles, inaddition or alternatively to slices such as video slices. Video may becoded using I, P or B tile groups and/or tiles.

Mode application unit 360 is configured to determine the predictioninformation for a video block of the current video slice by parsing themotion vectors or related information and other syntax elements, anduses the prediction information to produce the prediction blocks for thecurrent video block being decoded. For example, the mode applicationunit 360 uses some of the received syntax elements to determine aprediction mode (intra or inter-prediction) used to code the videoblocks of the video slice, an inter-prediction slice type (B slice, Pslice, or GPB slice), construction information for one or more of thereference picture lists for the slice, motion vectors for each interencoded video block of the slice, inter-prediction status for eachinter-coded video block of the slice, and other information to decodethe video blocks in the current video slice. The same or similar may beapplied for or by embodiments using tile groups such as video tilegroups and/or tiles such as video tiles in addition or alternatively toslices such as video slices). Video may be coded using I, P or B tilegroups and/or tiles.

Embodiments of the video decoder 30 as shown in FIG. 3 may be configuredto partition and/or decode the picture by using slices (also referred toas video slices), for which a picture may be partitioned into, ordecoded using, one or more slices (typically non-overlapping). Eachslice may comprise one or more blocks (e.g., CTUs) or one or more groupsof blocks (e.g., tiles (H.265/HEVC and VVC) or bricks (VVC)).

Embodiments of the video decoder 30 as shown in FIG. 3 may be configuredto partition and/or decode the picture by using slices/tile groups (alsoreferred to as video tile groups) and/or tiles (also referred to asvideo tiles), for which a picture may be partitioned into or decodedusing one or more slices/tile groups (typically non-overlapping), andeach slice/tile group may comprise one or more blocks (e.g., CTUs) orone or more tiles, wherein each tile may be of rectangular shape and maycomprise one or more blocks or CTUs to form complete or fractionalblocks.

Other variations of the video decoder 30 might be used to decode theencoded picture data 21. For example, the decoder 30 can produce theoutput video stream without the loop filtering unit 320. For example, anon-transform based decoder 30 can inverse-quantize the residual signaldirectly without the inverse-transform processing unit 312 for certainblocks or frames. In another implementation, the video decoder 30 canhave the inverse-quantization unit 310 and the inverse-transformprocessing unit 312 combined into a single unit. It should be understoodthat, in the encoder 20 and the decoder 30, a processing result of acurrent step may be further processed and then output to the next step.For example, after interpolation filtering, motion vector derivation orloop filtering, a further operation, such as Clip or shift, may beperformed on the processing result of the interpolation filtering,motion vector derivation or loop filtering.

It should be noted that further operations may be applied to the derivedmotion vectors of current block (including but not limit to controlpoint motion vectors of affine mode, sub-block motion vectors in affine,planar, ATMVP modes, temporal motion vectors, and so on). For example,the value of motion vector is constrained to a predefined rangeaccording to its representing bit. If the representing bit of motionvector is bitDepth, then the range is −2{circumflex over( )}(bitDepth-1)˜2{circumflex over ( )}(bitDepth-1)-1, where“{circumflex over ( )}” means exponentiation. For example, if bitDepthis set equal to 16, the range is −32768˜32767; if bitDepth is set equalto 18, the range is −13107˜131071. For example, the value of the derivedmotion vector (e.g. the MVs of four 4×4 sub-blocks within one 8×8 block)is constrained such that the max difference between integer parts of thefour 4×4 sub-block MVs is no more than N pixels, such as no more than 1pixel. Here provides two methods for constraining the motion vectoraccording to the bitDepth.

FIG. 4 is a schematic diagram of a video coding device 400 according toan embodiment of the disclosure. The video coding device 400 is suitablefor implementing the disclosed embodiments as described herein. In anembodiment, the video coding device 400 may be a decoder such as videodecoder 30 of FIG. 1A or an encoder such as video encoder 20 of FIG. 1A.The video coding device 400 comprises ingress ports 410 (or input ports410) and receiver units (Rx) 420 for receiving data; a processor, logicunit, or central processing unit (CPU) 430 to process the data;transmitter units (Tx) 440 and egress ports 450 (or output ports 450)for transmitting the data; and a memory 460 for storing the data. Thevideo coding device 400 may also comprise optical-to-electrical (OE)components and electrical-to-optical (EO) components coupled to theingress ports 410, the receiver units 420, the transmitter units 440,and the egress ports 450 for egress or ingress of optical or electricalsignals.

The processor 430 is implemented by hardware and software. The processor430 may be implemented as one or more CPU chips, cores (e.g., as amulti-core processor), FPGAs, ASICs, and DSPs. The processor 430 is incommunication with the ingress ports 410, receiver units 420,transmitter units 440, egress ports 450, and memory 460. The processor430 comprises a coding module 470. The coding module 470 implements thedisclosed embodiments described above. For instance, the coding module470 implements, processes, prepares, or provides the various codingoperations. The inclusion of the coding module 470 therefore provides asubstantial improvement to the functionality of the video coding device400 and effects a transformation of the video coding device 400 to adifferent state. Alternatively, the coding module 470 is implemented asinstructions stored in the memory 460 and executed by the processor 430.The memory 460 may comprise one or more disks, tape drives, andsolid-state drives and may be used as an over-flow data storage device,to store programs when such programs are selected for execution, and tostore instructions and data that are read during program execution. Thememory 460 may be, for example, volatile and/or non-volatile and may bea read-only memory (ROM), random access memory (RAM), ternarycontent-addressable memory (TCAM), and/or static random-access memory(SRAM).

FIG. 5 is a simplified block diagram of an apparatus 500 that may beused as either or both of the source device 12 and the destinationdevice 14 from FIG. 1 according to an exemplary embodiment. A processor502 in the apparatus 500 might be a central processing unit.Alternatively, the processor 502 might be any other type of device, ormultiple devices, capable of manipulating or processing informationnow-existing or hereafter developed. Although the disclosedimplementations might be practiced with a single processor as shown,e.g., the processor 502, advantages in speed and efficiency might beachieved using more than one processor. A memory 504 in the apparatus500 might be a read only memory (ROM) device or a random access memory(RAM) device in an implementation. Any other suitable type of storagedevice might be used as the memory 504. The memory 504 can include codeand data 506 that is accessed by the processor 502 using a bus 512. Thememory 504 can further include an operating system 508 and applicationprograms 510, the application programs 510 including at least oneprogram that permits the processor 502 to perform the methods describedhere. For example, the application programs 510 can include applications1 through N, which further include a video coding application thatperforms the methods described here. The apparatus 500 can also includeone or more output devices, such as a display 518. The display 518 maybe, in one example, a touch sensitive display that combines a displaywith a touch sensitive element that is operable to sense touch inputs.The display 518 might be coupled to the processor 502 via the bus 512.

Although depicted here as a single bus, the bus 512 of the apparatus 500might be composed of multiple buses. Further, the secondary storage 514might be directly coupled to the other components of the apparatus 500or might be accessed via a network and can comprise a single integratedunit such as a memory card or multiple units such as multiple memorycards. The apparatus 500 can thus be implemented in a wide variety ofconfigurations. Current hybrid video codecs employ predictive coding. Apicture of a video sequence is subdivided into blocks of pixels andthese blocks are then coded. Instead of coding a block pixel by pixel,the entire block is predicted using previously encoded pixels in thespatial or temporal proximity of the block. The encoder furtherprocesses only the differences between the block and its prediction. Thefurther processing typically includes a transformation of the blockpixels into coefficients in a transformation domain. The coefficientsmay then be further compressed (e.g., by means of quantization) andfurther compacted (e.g., by entropy coding) to form a bitstream. Thebitstream can further include any signaling information which enablesthe decoder to decode the encoded video. For instance, the signaling mayinclude settings concerning the encoder settings such as size of theinput picture, frame rate, quantization step indication, predictionapplied to the blocks of the pictures, or the like.

The differences between a block and its prediction are known as theresidual of the block. More specifically, each pixel of the block has aresidual, which is the difference between an intensity level of thatpixel and its predicted intensity level. The intensity level of a pixelis referred to as the pixel value or value of the pixel. The residualsof all the pixels of a block are referred to collectively as theresidual of the block. In other words, the block has a residual which isa set or matrix comprises the residuals of all the pixels of the block.Temporal prediction exploits temporal correlation between pictures, alsoreferred to as frames, of a video. The temporal prediction is alsocalled inter-prediction, as it is a prediction using the dependenciesbetween (inter) different video frames. Accordingly, a block to bedecoded, also referred to as a current block, is predicted from one ormore previously decoded pictures referred to as reference pictures. Theone or more reference pictures are not necessarily pictures precedingthe current picture in which the current block is located in thedisplaying order of the video sequence. The encoder may encode thepictures in a coding order different from the displaying order. As aprediction of the current block, a co-located block (referred to as apredictor) in a reference picture may be determined. The co-locatedblock may be located in the reference picture on the same position asthe current block in the current picture. Such prediction is accuratefor motionless picture regions, i.e., picture regions without movementfrom one picture to another.

In the encoder, in order to obtain a predictor which takes movement intoaccount, i.e., a motion compensated predictor, motion estimation istypically employed. The current block is predicted by a block located inthe reference picture at a position indicated by a motion vector. Themotion vector points from the position of the co-located block to theposition of the current block (or vice versa, depending on the signconvention). In order to enable a decoder to determine the sameprediction of the current block as the encoder, the motion vector may besignaled in the bitstream. In order to further reduce the signalingoverhead caused by signaling the motion vector for each of the blocks,the motion vector itself may be estimated. The motion vector estimationmay be performed based on the motion vectors of blocks which areneighbors of the current block in spatial and/or temporal domain.

The prediction of the current block may be computed using one referencepicture or by weighting predictions obtained from two or more referencepictures. The reference picture may be an adjacent picture, i.e., apicture immediately preceding or immediately following the currentpicture in the display order since adjacent pictures are most likely tobe similar to the current picture. The reference picture may also be anypicture preceding or following the current picture in the displayingorder and preceding the current picture in the bitstream (decodingorder). This may provide advantages for instance in case of occlusionsand/or non-linear movement in the video content. The reference picturemay be signaled in the bitstream.

A special mode of the inter-prediction is a so-called bi-prediction inwhich two reference pictures are used in generating the prediction ofthe current block. In particular, two predictions determined in therespective two reference pictures are combined into a prediction signalof the current block. The bi-prediction can result in a more accurateprediction of the current block than the uni-prediction, i.e.,prediction only using a single reference picture. The more accurateprediction leads to smaller differences between the pixels of thecurrent block and the prediction to smaller residuals, which may beencoded more efficiently, i.e., less coding bits. In order to providemore accurate motion estimation, the resolution of the reference picturemay be enhanced, for example by interpolating samples between pixels.Fractional pixel interpolation can be performed by weighted averaging ofthe closest pixels. For example, in case of half-pixel resolution, abilinear interpolation can be used. Other fractional pixels can becalculated as an average of the closest pixels weighted by, for example,the inverse of the distance between the respective closest pixels to thepixel being predicted.

A motion vector can be estimated, for example, by calculating asimilarity between the current block and the corresponding predictionblocks pointed to by candidate motion vectors in the reference picture.In order to reduce the complexity, the number of candidate motionvectors can be reduced by limiting the candidate motion vectors to acertain search space. The search space may be, for instance, defined bya number and/or positions of pixels surrounding the position in thereference picture corresponding to the position of the current block inthe current image. Alternatively, the candidate motion vectors may bedefined by a list of candidate motion vectors formed of motion vectorsof neighboring blocks. Motion vectors are usually at least partiallydetermined at the encoder side and signaled to the decoder within thecoded bitstream. The motion vectors may also be derived at the decoder.In such case, the current block is not available at the decoder andcannot be used for calculating the similarity between the current blockand any of the blocks to which the candidate motion vectors point in thereference picture. Therefore, instead of the current block, a templatecan be used which can be constructed out of pixels of previously decodedblocks. For instance, previously decoded pixels adjacent to the currentblock may be used. Such motion estimation provides an advantage ofreducing the signaling: the motion vector is derived in the same way atboth the encoder and the decoder and thus, no signaling is needed. Onthe other hand, the accuracy of such motion estimation may be lower.

In order to provide a tradeoff between the accuracy and signalingoverhead, the motion vector estimation may be divided into two steps:motion vector derivation and motion vector refinement. For instance, amotion vector derivation may include selection of a motion vector fromthe list of candidates. The selected motion vector may be furtherrefined, for instance, by a search within a search space. The search inthe search space is based on calculating a cost function for eachcandidate motion vector, i.e., for each candidate position of the blockto which the candidate motion vector points.

Document JVET-D0029: Decoder-Side Motion Vector Refinement Based onBilateral Template Matching, X. Chen, J. An, J. Zheng (The document canbe found at: http://phenix.it-sudparis.eu/jvet/site) shows motion vectorrefinement in which a first motion vector in integer pixel resolution isfound and further refined by a search with a half-pixel resolution in asearch space around the first motion vector. Here, the pixel resolution(e.g., integer or half-integer) describes the resolution of the searchspace, i.e., the displacement of the searched points to the non-refinedmotion vector that is input to the process. As a result, the searchcoordinates of the refinement stage do not necessarily coincide with theactual pixel coordinates on the image plane. The motion vectorrefinement may be performed at the decoder without assistance from theencoder. The decoder loop in the encoder may employ the same refinementto obtain corresponding reference pictures. The refinement can beperformed by determining a template, determining a search space, andfinding in the search space the position of a reference picture portionbest matching the template. The best matching portion positiondetermines the best motion vector which is then used to obtain thepredictor of the current block, i.e., the current block beingreconstructed.

In an embodiment, as shown in FIG. 6, an inter-prediction methodcomprising:

S601: obtaining an initial motion vector for a current block. An initialmotion vector MV0, which can be seen as a first estimate orapproximation of the exact motion vector, is obtained. For instance, MV0may be selected from a list of candidate motion vectors. The list mayinclude motion vectors of at least one block adjacent to the currentblock. Alternatively, MV0 may be obtained by block matching at theencoder side and signaled to the decoder side within the bitstream.Correspondingly, at the decoder side, the initial motion vector MV0might be obtained from the bitstream. For instance, an index to the listof candidates is extracted from the bitstream and the motion vectorcandidate identified by that index is provided as the initial motionvector MV0.

Alternatively, coordinates of MV0 are directly extracted from thebitstream. It is noted that the present application is not limited toany particular way of obtaining the initial motion vector MV0. Forexample, the MV0 may be determined by template matching in the same wayat the encoder and the decoder. And alternatively, the motion vector maybe predicted as a function of motion vectors of the neighboring block ofthe current block in the spatial or temporal domain.

The initial motion vector MV0 is an initial estimate of a final motionvector MV0″ to be used in inter-prediction of a current block. Itconstitutes the input for a refinement process at the end of which thefinal motion vector MV0″ is output.

S602: determining search space positions according to the initial motionvector.

Assuming search space positions comprise the central search positionsand neighboring search space positions, and wherein the central searchspace position is pointed to by the initial motion vector. In animplementation, the step S602 comprises determining the central searchspace position according to the initial motion vector, and determiningthe neighboring search space positions according to one or more presetoffsets and the central search space position.

In an implementation, a search space consists of the search spacepositions, and a pattern of the search space is a 5×5 search spaceposition square. As an example, the search space is constructedaccording to the initial motion vector MV0 and one or more candidatemotion vectors relate to the initial motion vector. Then the motionvector MV0″ (corresponding to coordinates of a search space position) isselected according to the matching cost from the initial motion vectorMV0 and the one or more candidate motion vectors.

(S603) It is noted that for some candidate motion vectors of the searchspace might be for all candidate motion vectors of the respectivepartial search spaces determined in each of the stages. In differentembodiments of the present application, the costs may be calculated as apart of and during the search space construction.

In an implementation, the candidate motion vectors for the current blockpoint from the top left pixel of the current block in the currentpicture to the respective top left pixels of candidate prediction blocksin the reference picture. The top left pixels of the candidateprediction blocks thus represent the search space in the referencepicture. The top left pixel of a block is taken as the position of theblock. It is noted that any other pixel of a block can be taken as theposition of the block, wherein it is understood that the same positionconvention applies to all blocks. For example, a motion vector may bedefined equivalently as running from a center pixel of the current blockto the center pixel of a respective candidate block.

It is noted that every candidate motion vector, including the initialmotion vector, points to a pixel in the reference picture, which is asearch space position. And the coordinate position relationship betweenpixels pointed by the initial motion vector and by other candidatemotion vectors might be represented by one or more motion vector offsetsbetween the initial motion vector and the other candidate motionvectors. The one or more motion vector offsets might be predeterminedsuch that the location relationship between the central search positionsand neighboring search space positions might be predetermined.

S603: checking matching costs of the search space positions according toa checking order to select a target search space position with a minimalmatching cost.

In an implementation, checking a match cost of each of the search spacepositions in turn according to the checking order; and selecting asearch space position with the minimal matching cost among the searchspace positions as the target search space position.

The matching cost may be measured by a cost function which may, forexample, be a sum of absolute differences between the template and thereference picture area that corresponds to the template in the locationpointed to by the motion vector candidate. After calculating the sum ofabsolute differences (SAD) for all candidate motion vectors, thecandidate with the smallest SAD is selected. It is noted that SAD isonly an example. The cost function can be SAD (sum of absolutedifferences), MRSAD (Mean removed sum of absolute differences), SSE (Sumof squared errors), or any other cost function for representing asimilarity. The best motion vector is selected based on the comparisonsamong the matching costs of the search space positions.

In an implementation, a match cost of one of the search space positionsis compared with a temp minimal matching cost. The match cost of the oneof the search space positions is set as the temp minimal matching costwhen the match cost of the one of the search space positions is smallerthan the temp minimal matching cost. The temp minimal matching cost isset as the minimal matching cost after the last one of the search spacepositions is checked.

In an embodiment, the search space might be a square pattern, as shownin FIG. 7. As an example, the pixel pointed to by the initial motionvector is considered as (0, 0) of a coordinate system. And in thecoordinate system, horizontal right is considered as a horizontalpositive direction and vertical down is considered as a verticalpositive direction. The search space might comprise 25 search spacepositions. And pixels with the coordinates (−2, −2), (2, 2), (−2, 2) and(2, −2) are corners of the square pattern. The 25 search space positionsare divided into one or more groups to define the checking order. And itis noted that according to the different embodiments, the step ofdividing the search space positions into one or more groups might not benecessary, which is only for clearly describing the design of a kind ofchecking order is determined. In a first embodiment, the 25 search spacepositions is divided into two groups:

-   -   Group I: (0, 0);    -   Group II: all other search space positions.

As shown in FIG. 8, the number of each search space position representsthe order of each search space positions according to the checkingorder, and a position marked with the smaller number is checked earlierthan a position marked with the larger number. The position (0, 0)marked as “1” is checked first, then other search space positions inGroup II are checked according to a horizontal checking order (from leftto right, line by line). Therefore, the checking order is (0, 0), (−2,−2), (−1, −2), (0, −2), (1, −2), (2, −2), (−2, −1), (−1, −1), (0, −1),(1, −1), (2, −1), (−2, 0), (−1, 0), (1, 0), (2, 0), (−2, 1), (−1, 1),(0, 1), (1, 1), (2, 1), (−2, 2), (−1, 2), (0, 2), (1, 2), (2, 2). It isnoted that the search space positions in Group II might also be checkedaccording to other checking order, like a vertical checking order (fromtop to bottom, column by column), a zig-zag checking order and so on.The central position of the search space is checked first, then othersearch space positions are checked based on a preset checking order. Italso can be implemented based on a non-square pattern search space. Asan example, it might be a cross-shaped pattern with 21 search spacepositions, corresponds to a checking order illustrated as FIG. 9. Asanother example, it might be a Union flag pattern with 17 search spacepositions, corresponds to a checking order illustrated as FIG. 10.

In a second embodiment, the Group II can be further divided into moregroups, for example, the 25 search space positions is divided into fourgroups:

-   -   Group I: (0, 0);    -   Group II: (−1, 0), (0, 1), (1, 0), (0, −1) (neighboring        positions of the central position on vertical or horizontal        direction);    -   Group III: (−1,−1), (−1, 1), (1, 1), (1, −1) (Positions are 1        pixel sample away from the central position and are not        comprised in the second group);    -   Group IV: all other search space positions.

Group I, II, III and IV are checked in turn. It is noted that thechecking order within a same group is not limited, for example, forGroup II, the checking order might be (−1, 0), (0, 1), (1, 0), (0, −1)or (−1, 0), (1, 0), (0, 1), (0, −1). It is also noted that the searchspace positions in Group IV might also be checked according to differentchecking orders (like clockwise or counterclockwise) and with differentstarting checking point (like top-left pixel of the search space orother position in Group IV). As an example of FIG. 7, the checking orderis (0, 0), (−1, 0), (0, 1), (1, 0), (0, −1), (−1, −1), (−1, 1), (1, 1),(1, −1), (−2, 0), (−2, 1), (−2, 2), (−1, 2), (0, 2), (1, 2), (2, 2), (2,1), (2, 0), (2, −1), (2, −2), (1, −2), (0, −2), (−1, −2), (−2, −2), (−2,−1). The checking order can also be implemented based on other patternsearch space. As an example, it might be a diamond pattern with 13search space positions, corresponds to a checking order illustrated asFIG. 11.

In a third specific embodiment, the Group IV can be further divided intomore groups, for example, the 25 search space positions can be dividedinto five groups:

-   -   Group I: (0, 0);    -   Group II: (−1, 0), (0, 1), (1, 0), (0, −1) (neighboring        positions of the central position on vertical or horizontal        direction);    -   Group III: (−1,−1), (−1, 1), (1, 1), (1, −1) (Positions are 1        pixel sample away from the central position and are not        comprised in the second group);    -   Group IV: (−2, 0), (0, 2), (2, 0), (0, −2) (Positions are 2        pixel samples away from the central position on a        vertical/horizontal direction and 0 pixel sample away from the        central position on the other horizontal/vertical direction);    -   Group V: all other search space positions.

As shown in FIG. 12, as an example, the checking order is (0, 0), (−1,0), (0, 1), (1, 0), (0, −1), (−1, −1), (−1, 1), (1, 1), (1, −1), (−2,0), (0, 2), (2, 0), (0, −2), (−2, −1), (−2, 1), (−2, 2), (−1, 2), (1,2), (2, 2), (2, 1), (2, −1), (2, −2), (1, −2), (−1, −2), (−2, −2).

In a fourth embodiment, the Group V can be further divided into moregroups, for example, the 25 search space positions is divided into sixgroups:

-   -   Group I: (0, 0);    -   Group II: (−1, 0), (0, 1), (1, 0), (0, −1) (neighboring        positions of the central position on vertical or horizontal        direction);    -   Group III: (−1,−1), (−1, 1), (1, 1), (1, −1) (Positions are 1        pixel sample away from the central position and are not        comprised in the second group);    -   Group IV: (−2, 0), (0, 2), (2, 0), (0, −2) (Positions are 2        pixel samples away from the central position on a        vertical/horizontal direction and 0 pixel sample away from the        central position on the other horizontal/vertical direction);    -   Group V: (−2, −2), (−2, 2), (2, 2), (2, −2) (Positions are 2        pixel samples away from the central position on both vertical        and horizontal direction);    -   Group VI: all other search space positions.

As shown in FIG. 13, as an example, the checking order is (0, 0), (−1,0), (0, 1), (1, 0), (0, −1), (−1, −1), (−1, 1), (1, 1), (1, −1), (−2,0), (0, 2), (2, 0), (0, −2), (−2, −2), (−2, 2), (2, 2), (2, −2), (−2,−1), (−2, 1), (−1, 2), (1, 2), (2, 1), (2, −1), (1, −2), (−1, −2).

In a fifth embodiment, the 25 search space positions are not divided.They are checked according to a preset checking order, for example, ahorizontal checking order. As shown in FIG. 14, as an example, thechecking order is (−2, −2), (−1, −2), (0, −2), (1, −2), (2, −2), (−2,−1), (−1, −1), (0, −1), (1, −1), (2, −1), (−2, 0), (−1, 0), (0, 0), (1,0), (2, 0), (−2, 1), (−1, 1), (0, 1), (1, 1), (2, 1), (−2, 2), (−1, 2),(0, 2), (1, 2), (2, 2).

S604: Determining a refining motion vector of the current block based onthe initial motion vector and the target search space position. Arefining motion vector MV0″ is a motion vector pointing to the targetsearch space position. And the offset between the target search spaceposition and the central search space position can be derived first,then the refining motion vector MV0″ might be also derived by adding theinitial motion vector and the offset.

FIG. 15 shows an inter-prediction apparatus 1500 of the presentapplication. The inter-prediction apparatus 1500, comprising: anobtaining module 1501, configured to obtain an initial motion vector fora current block; a setting module 1502, configured to determine searchspace positions according to the initial motion vector; a calculatingmodule 1503, configured to check matching costs of the search spacepositions according to a checking order to select a target search spaceposition with a minimal matching cost; and a prediction module 1504,configured to determine a refining motion vector of the current blockbased on the initial motion vector and the target search space position,wherein a central search space position is checked first according tothe checking order, and wherein the central search space position ispointed to by the initial motion vector.

In an implementation, search space positions comprise the central searchpositions and neighboring search space positions, wherein the settingmodule 1502 is configured to determine the central search space positionaccording to the initial motion vector, and determine the neighboringsearch space positions according to one or more preset offsets and thecentral search space position.

In an implementation, a search space consists of the search spacepositions, and a pattern of the search space is a 5×5 search spaceposition square.

In another implementation, the calculating module 1503 is configured tocheck a match cost of each of the search space positions in turnaccording to the checking order, and to select a search space positionwith the minimal matching cost among the search space positions as thetarget search space position.

In an implementation, the calculating module 1503 is configured tocompare a match cost of one of the search space positions with a tempminimal matching cost, set the match cost of the one of the search spacepositions as the temp minimal matching cost when the match cost of theone of the search space positions is smaller than the temp minimalmatching cost, and to set the temp minimal matching cost as the minimalmatching cost after the last one of the search space positions ischecked.

In an implementation, the central search space position is set as (0, 0)of a coordinate system, horizontal right is set as a horizontal positivedirection and vertical down is set as a vertical positive direction.

In an implementation, the checking order is (0, 0), (−2, −2), (−1, −2),(0, −2), (1, −2), (2, −2), (−2, −1), (−1, −1), (0, −1), (1, −1), (2,−1), (−2, 0), (−1, 0), (1, 0), (2, 0), (−2, 1), (−1, 1), (0, 1), (1, 1),(2, 1), (−2, 2), (−1, 2), (0, 2), (1, 2), (2, 2).

In an implementation, the checking order is (0, 0), (−1, 0), (0, 1), (1,0), (0, −1), (−1, −1), (−1, 1), (1, 1), (1, −1), (−2, 0), (−2, 1), (−2,2), (−1, 2), (0, 2), (1, 2), (2, 2), (2, 1), (2, 0), (2, −1), (2, −2),(1, −2), (0, −2), (−1, −2), (−2, −2), (−2, −1).

In an implementation, the checking order is (0, 0), (−1, 0), (0, 1), (1,0), (0, −1), (−1, −1), (−1, 1), (1, 1), (1, −1), (−2, 0), (0, 2), (2,0), (0, −2), (−2, −1), (−2, 1), (−2, 2), (−1, 2), (1, 2), (2, 2), (2,1), (2, −1), (2, −2), (1, −2), (−1, −2), (−2, −2).

In another implementation, the checking order is (0, 0), (−1, 0), (0,1), (1, 0), (0, −1), (−1, −1), (−1, 1), (1, 1), (1, −1), (−2, 0), (0,2), (2, 0), (0, −2), (−2, −2), (−2, 2), (2, 2), (2, −2), (−2, −1), (−2,1), (−1, 2), (1, 2), (2, 1), (2, −1), (1, −2), (−1, −2).

FIG. 16 shows an inter-prediction apparatus 1600 of the presentapplication, the apparatus 1600 may be in the form of a decoder or anencoder. The apparatus 1600 includes one or more processors 1601 and anon-transitory computer-readable storage medium 1602 coupled to theprocessors and storing programming for execution by the processors,wherein the programming, when executed by the processors, configures thedecoder to carry out the method in FIG. 6.

In another embodiment, a computer program product comprising programcode for performing the method in FIG. 6 when executed on a computer ora processor.

In another embodiment, a non-transitory computer-readable mediumcarrying a program code which, when executed by a computer device,causes the computer device to perform the method in FIG. 6.

Following is an explanation of the applications of the encoding methodas well as the decoding method as shown in the above-mentionedembodiments, and a system using them.

FIG. 17 is a block diagram showing a content supply system 3100 forrealizing content distribution service. This content supply system 3100includes capture device 3102, terminal device 3106, and optionallyincludes display 3126. The capture device 3102 communicates with theterminal device 3106 over communication link 3104. The communicationlink may include the communication channel 13 described above. Thecommunication link 3104 includes but not limited to WIFI, Ethernet,Cable, wireless (3G/4G/5G), USB, or any kind of combination thereof, orthe like.

The capture device 3102 generates data, and may encode the data by theencoding method as shown in the above embodiments. Alternatively, thecapture device 3102 may distribute the data to a streaming server (notshown in the Figures), and the server encodes the data and transmits theencoded data to the terminal device 3106. The capture device 3102includes but not limited to camera, smart phone or Pad, computer orlaptop, video conference system, PDA, vehicle mounted device, or acombination of any of them, or the like. For example, the capture device3102 may include the source device 12 as described above. When the dataincludes video, the video encoder 20 included in the capture device 3102may actually perform video encoding processing. When the data includesaudio such as voice, an audio encoder included in the capture device3102 may perform audio encoding processing. For some scenarios, thecapture device 3102 distributes the encoded video and audio data bymultiplexing them together. For other scenarios, for example in thevideo conference system, the encoded audio data and the encoded videodata are not multiplexed. Capture device 3102 separately distributes theencoded audio data and the encoded video data to the terminal device3106.

In the content supply system 3100, the terminal device 310 receives andreproduces the encoded data. The terminal device 3106 could be a devicewith data receiving and recovering capability, such as smart phone orPad 3108, computer or laptop 3110, network video recorder (NVR)/digitalvideo recorder (DVR) 3112, TV 3114, set top box (STB) 3116, videoconference system 3118, video surveillance system 3120, personal digitalassistant (PDA) 3122, vehicle mounted device 3124, or a combination ofany of them, or the like capable of decoding the above-mentioned encodeddata. For example, the terminal device 3106 may include the destinationdevice 14 as described above. When the encoded data includes video, thevideo decoder 30 included in the terminal device is prioritized toperform video decoding. When the encoded data includes audio, an audiodecoder included in the terminal device is prioritized to perform audiodecoding processing.

For a terminal device with its display (examples of terminal devicesincluding, for example, smart phone or Pad 3108, computer or laptop3110, network video recorder (NVR)/digital video recorder (DVR) 3112, TV3114, personal digital assistant (PDA) 3122, or vehicle mounted device3124), the terminal device can feed the decoded data to its display. Fora terminal device not equipped with no display (examples including STB3116, video conference system 3118, or video surveillance system 3120),the terminal device can be connected to an external display 3126 toreceive and show the decoded data.

When each device in this system performs encoding or decoding, thepicture encoding device or the picture decoding device, as shown in theabove-mentioned embodiments, might be used. FIG. 18 is a diagram showinga structure of an example of the terminal device 3106. After theterminal device 3106 receives stream from the capture device 3102, theprotocol proceeding unit 3202 analyzes the transmission protocol of thestream. The protocol includes but not limited to Real Time StreamingProtocol (RTSP), Hyper Text Transfer Protocol (HTTP), HTTP Livestreaming protocol (HLS), MPEG-DASH, Real-time Transport protocol (RTP),Real Time Messaging Protocol (RTMP), or any kind of combination thereof,or the like.

After the protocol proceeding unit 3202 processes the stream, a streamfile is generated. The stream file is outputted to a demultiplexing unit3204. The demultiplexing unit 3204 can separate the multiplexed datainto the encoded audio data and the encoded video data. As describedabove, for some practical scenarios, for example in the video conferencesystem, the encoded audio data and the encoded video data are notmultiplexed. In this situation, the encoded data is transmitted to videodecoder 3206 and audio decoder 3208 without through the demultiplexingunit 3204. Via the demultiplexing processing, video elementary stream(ES), audio ES, and optionally subtitles are generated. The videodecoder 3206, which includes the video decoder 30 as explained in theabove-mentioned embodiments, decodes the video ES by the decoding methodas shown in the above-mentioned embodiments to generate video frame, andfeeds this data to the synchronous unit 3212. The audio decoder 3208,decodes the audio ES to generate audio frame, and feeds this data to thesynchronous unit 3212. Alternatively, the video frame may store in abuffer (not shown in FIG. 18) before feeding it to the synchronous unit3212. Similarly, the audio frame may store in a buffer (not shown inFIG. 20) before feeding it to the synchronous unit 3212.

The synchronous unit 3212 synchronizes the video frame and the audioframe, and supplies the video/audio to a video/audio display 3214. Forexample, the synchronous unit 3212 synchronizes the presentation of thevideo and audio information. Information may code in the syntax usingtime stamps concerning the presentation of coded audio and visual dataand time stamps concerning the delivery of the data stream itself. Ifsubtitle is included in the stream, the subtitle decoder 3210 decodesthe subtitle, and synchronizes it with the video frame and the audioframe, and supplies the video/audio/subtitle to a video/audio/subtitledisplay 3216.

The present application is not limited to the above-mentioned system,and either the picture encoding device or the picture decoding device inthe above-mentioned embodiments might be incorporated into other system,for example, a car system.

Mathematical Operators

The mathematical operators used in this application are similar to thoseused in the C programming language. However, the results of integerdivision and arithmetic shift operations are defined more precisely, andadditional operations are defined, such as exponentiation andreal-valued division. Numbering and counting conventions generally beginfrom 0, e.g., “the first” is equivalent to the 0-th, “the second” isequivalent to the 1-th, etc.

Arithmetic Operators

The following arithmetic operators are defined as follows:

-   -   + Addition    -   − Subtraction (as a two-argument operator) or negation (as a        unary prefix operator)    -   * Multiplication, including matrix multiplication    -   x^(y) Exponentiation. Specifies x to the power of y. In other        contexts, such notation is used for superscripting not intended        for interpretation as exponentiation.    -   / Integer division with truncation of the result toward zero.        For example, 7/4 and −7/−4 are truncated to 1 and −7/4 and 7/−4        are truncated to −1.    -   ÷ Used to denote division in mathematical equations where no        truncation or rounding is intended.

$\frac{x}{y}$

-   -   Used to denote division in mathematical equations where no        truncation or rounding is intended.

$\sum\limits_{i = x}^{y}$

f(i) The summation of f(i) with i taking all integer values from x up toand including y.

-   -   x % y Modulus. Remainder of x divided by y, defined only for        integers x and y with x>=0 and y>0.        Logical Operators

The following logical operators are defined as follows:

-   -   x && y Boolean logical “and” of x and y    -   x∥y Boolean logical “or” of x and y    -   ! Boolean logical “not”    -   x?y:z If x is TRUE or not equal to 0, evaluates to the value of        y; otherwise, evaluates to the value of z.        Relational Operators

The following relational operators are defined as follows:

-   -   > Greater than    -   >= Greater than or equal to    -   < Less than    -   <= Less than or equal to    -   == Equal to    -   != Not equal to

When a relational operator is applied to a syntax element or variablethat has been assigned the value “na” (not applicable), the value “na”is treated as a distinct value for the syntax element or variable. Thevalue “na” is considered not to be equal to any other value.

Bit-Wise Operators

The following bit-wise operators are defined as follows:

-   -   & Bit-wise “and”. When operating on integer arguments, operates        on a two's complement representation of the integer value. When        operating on a binary argument that contains fewer bits than        another argument, the shorter argument is extended by adding        more significant bits equal to 0.    -   | Bit-wise “or”. When operating on integer arguments, operates        on a two's complement representation of the integer value. When        operating on a binary argument that contains fewer bits than        another argument, the shorter argument is extended by adding        more significant bits equal to 0.    -   {circumflex over ( )} Bit-wise “exclusive or”. When operating on        integer arguments, operates on a two's complement representation        of the integer value. When operating on a binary argument that        contains fewer bits than another argument, the shorter argument        is extended by adding more significant bits equal to 0.    -   x>>y Arithmetic right shift of a two's complement integer        representation of x by y binary digits. This function is defined        only for non-negative integer values of y. Bits shifted into the        most significant bits (MSBs) as a result of the right shift have        a value equal to the MSB of x prior to the shift operation.    -   x<<y Arithmetic left shift of a two's complement integer        representation of x by y binary digits. This function is defined        only for non-negative integer values of y. Bits shifted into the        least significant bits (LSBs) as a result of the left shift have        a value equal to 0.        Assignment Operators

The following arithmetic operators are defined as follows:

-   -   = Assignment operator    -   ++ Increment, i.e., x++ is equivalent to x=x+1; when used in an        array index, evaluates to the value of the variable prior to the        increment operation.    -   −− Decrement, i.e., x−− is equivalent to x=x−1; when used in an        array index, evaluates to the value of the variable prior to the        decrement operation.    -   += Increment by amount specified, i.e., x+=3 is equivalent to        x=x+3, and x+=(−3) is equivalent to x=x+(−3).    -   −= Decrement by amount specified, i.e., x−=3 is equivalent to        x=x−3, and x−=(−3) is equivalent to x=x−(−3).        Range Notation

The following notation is used to specify a range of values:

-   -   x=y . . . z x takes on integer values starting from y to z,        inclusive, with x, y, and z being integer numbers and z being        greater than y.        Mathematical Functions

The following mathematical functions are defined:

${{Abs}\;(x)} = \left\{ \begin{matrix}{x;} & {x>=0} \\{{- x};} & {x < 0}\end{matrix} \right.$

-   -   A sin (x) the trigonometric inverse sine function, operating on        an argument x that is in the range of −1.0 to 1.0, inclusive,        with an output value in the range of −π÷2 to π÷2, inclusive, in        units of radians    -   A tan (x) the trigonometric inverse tangent function, operating        on an argument x, with an output value in the range of −π÷2 to        π÷2, inclusive, in units of radians

${{Atan}\; 2\left( {y,x} \right)} = \left\{ \begin{matrix}{{{Atan}\left( \frac{y}{x} \right)};} & {x > 0} \\{{{{Atan}\left( \frac{y}{x} \right)} + \pi};} & {{x < 0}\&\&{y>=0}} \\{{{{Atan}\left( \frac{y}{x} \right)} - \pi};} & {{x < 0}\&\&{y < 0}} \\{{+ \frac{\pi}{2}};} & {{x==0}\&\&{y>=0}} \\{{- \frac{\pi}{2}};} & {otherwise}\end{matrix} \right.$

-   -   Ceil(x) the smallest integer greater than or equal to x.    -   Clip1_(Y)(x)=Clip3(0, (1<<BitDepth_(Y))−1, x)    -   Clip1_(C)(x)=Clip3(0, (1<<BitDepth_(C))−1, x)

${Cli{{p3}\left( {x,y,z} \right)}} = \left\{ \begin{matrix}{x;} & {z < x} \\{y;} & {z > y} \\{z;} & {otherwise}\end{matrix} \right.$

-   -   Cos (x) the trigonometric cosine function operating on an        argument x in units of radians.    -   Floor(x) the largest integer less than or equal to x.

${{GetCurrMsb}\left( {a,b,c,d} \right)} = \left\{ \begin{matrix}{{c + d}\ ;} & {{{b - a} >} = {d/2}} \\{{c - d}\ ;} & {{a - b} > {d/2}} \\{c;} & {otherwise}\end{matrix} \right.$

-   -   Ln(x) the natural logarithm of x (the base-e logarithm, where e        is the natural logarithm base constant 2.718 281 828 . . . ).    -   Log2(x) the base-2 logarithm of x.    -   Log 10(x) the base-10 logarithm of x.

${{Min}\left( {x,y} \right)} = \left\{ {{\begin{matrix}{x;} & {x<=y} \\{y;} & {x > y}\end{matrix}{{Max}\left( {x,y} \right)}} = \left\{ \begin{matrix}{x;} & {x>=y} \\{y;} & {x < y}\end{matrix} \right.} \right.$

-   -   Round(x)=Sign(x)*Floor(Abs(x)+0.5)

${{Sign}(x)} = \left\{ \begin{matrix}{{1;}\ } & {x > 0} \\{{0;}\ } & {x==0} \\{{{- 1};}\ } & {x < 0}\end{matrix} \right.$

-   -   Sin (x) the trigonometric sine function operating on an argument        x in units of radians    -   Sqrt(x)=√{square root over (x)}    -   Swap(x, y)=(y, x)    -   Tan (x) the trigonometric tangent function operating on an        argument x in units of radians        Order of Operation Precedence

When an order of precedence in an expression is not indicated explicitlyby use of parentheses, the following rules apply:

-   -   Operations of a higher precedence are evaluated before any        operation of a lower precedence.    -   Operations of the same precedence are evaluated sequentially        from left to right.

The table below specifies the precedence of operations from highest tolowest; a higher position in the table indicates a higher precedence.

For those operators that are also used in the C programming language,the order of precedence used in this Specification is the same as usedin the C programming language.

TABLE Operation precedence from highest (at top of table) to lowest (atbottom of table)   operations (with operands x, y, and z) “x++”, “x− −”“!x”, “−x” (as a unary prefix operator) x^(y) “x * y”, “x / y”, “x ÷ y”,“ x/y”, “x % y”${``{x + y}"},{{``{x - y}"}\mspace{14mu}\left( {{as}\mspace{14mu} a\mspace{14mu}{two}\text{-}{argument}\mspace{14mu}{operator}} \right)},{``{\sum\limits_{i = x}^{y}{f(i)}}"}$“x << y”, “x >> y” “x < y”, “x <= y”, “x > y”, “x >= y” “x = = y”, “x !=y” “x & y” “x | y” “x && y” “x | | y” “x ? y : z” “x..y” “x = y”, “x +=y”, “x −= y”Text Description of Logical Operations

In the text, a statement of logical operations as would be describedmathematically in the following form:

if( condition 0 )  statement 0 else if( condition 1 )  statement 1 ...else /* informative remark on remaining condition */  statement n may bedescribed in the following manner:  ... as follows / ... the followingapplies:  - If condition 0, statement 0  - Otherwise, if condition 1,statement 1  - ...  - Otherwise (informative remark on remainingcondition), statement n Each “If ... Otherwise, if ... Otherwise, ...”statement in the text is introduced with “... as follows” or “... thefollowing applies” immediately followed by “If ... ”. The last conditionof the “If ... Otherwise, if ... Otherwise, ...” is always an“Otherwise, ...”. Interleaved “If ... Otherwise, if ... Otherwise, ...”statements might be identified by matching “... as follows” or “... thefollowing applies” with the ending “Otherwise, ...”. In the text, astatement of logical operations as would be described mathematically inthe following form: if( condition 0a && condition 0b )  statement 0 elseif( condition 1a | | condition 1b )  statement 1 ... else  statement nmay be described in the following manner: ... as follows / ... thefollowing applies:  - If all of the following conditions are true,statement 0: - condition 0a - condition 0b  - Otherwise, if one or moreof the following conditions are true, statement 1: - condition 1a -condition 1b  - ...  - Otherwise, statement n In the text, a statementof logical operations as would be described mathematically in thefollowing form: if( condition 0)  statement 0 if( condition 1 ) statement 1 may be described in the following manner:  When condition0, statement 0  When condition 1, statement 1.

Embodiments of the encoder 20 and the decoder 30, and functionsdescribed herein may be implemented in hardware, software, firmware, orany combination thereof. If implemented in software, the functions maybe stored on a computer-readable medium or transmitted overcommunication media as one or more instructions or code and executed bya hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that might be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of non-limiting example, such computer-readable storage media cancomprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage,magnetic disk storage, or other magnetic storage devices, flash memory,or any other medium that might be used to store desired program code inthe form of instructions or data structures and that might be accessedby a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, thefunctionality described herein may be provided within dedicated hardwareand/or software modules configured for encoding and decoding, orincorporated in a combined codec. Also, the techniques could be fullyimplemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

The invention claimed is:
 1. An inter-prediction method for video block,comprising: obtaining an initial motion vector for a current block;determining search space positions according to the initial motionvector; checking matching costs for each of the search space positionsaccording to a checking order to select a target search space positionwith a minimal matching cost; and determining a refining motion vectorof the current block based on the initial motion vector and the targetsearch space position, wherein a central search space position ischecked first according to the checking order, and the central searchspace position is pointed to by the initial motion vector.
 2. The methodof claim 1, the search space positions comprising the central searchposition and neighboring search space positions, the determining searchspace positions comprising: determining the central search spaceposition according to the initial motion vector; and determining theneighboring search space positions according to one or more presetoffsets and the central search space position.
 3. The method of claim 2,comprising selecting a 5×5 search space position square as a pattern ofthe search space.
 4. The method of claim 1, wherein checking matchingcosts of the search space positions according to the checking ordercomprises: checking a match cost for each of the search space positionsaccording to the checking order; and selecting, from the search spacepositions as the target search space position, a search space positiondetermined to have the minimal matching cost.
 5. The method of claim 4,wherein checking the match cost of each of the search space positionscomprises: comparing a match cost of one of the search space positionswith a temp minimal matching cost; setting the match cost of the one ofthe search space positions as the temp minimal matching cost when thematch cost of the one of the search space positions is less than thetemp minimal matching cost; and setting the temp minimal matching costas the minimal matching cost after the last one of the search spacepositions is checked.
 6. The method of claim 1, wherein the centralsearch space position is set as (0, 0) of a coordinate system,horizontal right is set as a horizontal positive direction and verticaldown is set as a vertical positive direction.
 7. The method of claim 6,wherein the checking order is (0, 0), (−2, −2), (−1, −2), (0, −2), (1,−2), (2, −2), (−2, −1), (−1, −1), (0, −1), (1, −1), (2, −1), (−2, 0),(−1, 0), (1, 0), (2, 0), (−2, 1), (−1, 1), (0, 1), (1, 1), (2, 1), (−2,2), (−1, 2), (0, 2), (1, 2), (2, 2).
 8. The method of claim 6, whereinthe checking order is (0, 0), (−1, 0), (0, 1), (1, 0), (0, −1), (−1,−1), (−1, 1), (1, 1), (1, −1), (−2, 0), (−2, 1), (−2, 2), (−1, 2), (0,2), (1, 2), (2, 2), (2, 1), (2, 0), (2, −1), (2, −2), (1, −2), (0, −2),(−1, −2), (−2, −2), (−2, −1).
 9. The method of claim 6, wherein thechecking order is (0, 0), (−1, 0), (0, 1), (1, 0), (0, −1), (−1, −1),(−1, 1), (1, 1), (1, −1), (−2, 0), (0, 2), (2, 0), (0, −2), (−2, −1),(−2, 1), (−2, 2), (−1, 2), (1, 2), (2, 2), (2, 1), (2, −1), (2, −2), (1,−2), (−1, −2), (−2, −2).
 10. The method of claim 6, wherein the checkingorder is (0, 0), (−1, 0), (0, 1), (1, 0), (0, −1), (−1, −1), (−1, 1),(1, 1), (1, −1), (−2, 0), (0, 2), (2, 0), (0, −2), (−2, −2), (−2, 2),(2, 2), (2, −2), (−2, −1), (−2, 1), (−1, 2), (1, 2), (2, 1), (2, −1),(1, −2), (−1, −2).
 11. An inter-prediction apparatus, comprising: anobtaining module, configured to obtain an initial motion vector for acurrent block; a setting module, configured to determine search spacepositions according to the initial motion vector; a calculating module,configured to check matching costs of the search space positionsaccording to a checking order to select a target search space positionwith a minimal matching cost; and a prediction module, configured todetermine a refining motion vector of the current block based on theinitial motion vector and the target search space position and to checka central search space position first according to the checking order,and wherein the central search space position being pointed to by theinitial motion vector.
 12. The apparatus of claim 11, the search spacepositions comprising the central search positions and neighboring searchspace positions, the setting module being configured to: determine thecentral search space position according to the initial motion vector;and determine the neighboring search space positions according to one ormore preset offsets and the central search space position.
 13. Theapparatus of claim 12, a pattern of the search space comprising a 5×5search space position square.
 14. The apparatus of claim 11, thecalculating module being configured to: check a match cost for each ofthe search space positions according to the checking order; and select,as the target search space position from the search space positions, asearch space position with the minimal matching cost.
 15. The apparatusof claim 14, the calculating module being configured to: compare a matchcost of one of the search space positions with a temp minimal matchingcost; set the match cost of the one of the search space positions as thetemp minimal matching cost when the match cost of the one of the searchspace positions is smaller than the temp minimal matching cost; and setthe temp minimal matching cost as the minimal matching cost after thelast one of the search space positions is checked.
 16. The apparatus ofclaim 12, wherein the central search space position is set as (0, 0) ofa coordinate system, horizontal right is set as a horizontal positivedirection and vertical down is set as a vertical positive direction. 17.The apparatus of claim 16, wherein the checking order is (0, 0), (−2,−2), (−1, −2), (0, −2), (1, −2), (2, −2), (−2, −1), (−1, −1), (0, −1),(1, −1), (2, −1), (−2, 0), (−1, 0), (1, 0), (2, 0), (−2, 1), (−1, 1),(0, 1), (1, 1), (2, 1), (−2, 2), (−1, 2), (0, 2), (1, 2), (2, 2). 18.The apparatus of claim 16, wherein the checking order is (0, 0), (−1,0), (0, 1), (1, 0), (0, −1), (−1, −1), (−1, 1), (1, 1), (1, −1), (−2,0), (−2, 1), (−2, 2), (−1, 2), (0, 2), (1, 2), (2, 2), (2, 1), (2, 0),(2, −1), (2, −2), (1, −2), (0, −2), (−1, −2), (−2, −2), (−2, −1). 19.The apparatus of claim 16, wherein the checking order is (0, 0), (−1,0), (0, 1), (1, 0), (0, −1), (−1, −1), (−1, 1), (1, 1), (1, −1), (−2,0), (0, 2), (2, 0), (0, −2), (−2, −1), (−2, 1), (−2, 2), (−1, 2), (1,2), (2, 2), (2, 1), (2, −1), (2, −2), (1, −2), (−1, −2), (−2, −2). 20.The apparatus of claim 16, wherein the checking order is (0, 0), (−1,0), (0, 1), (1, 0), (0, −1), (−1, −1), (−1, 1), (1, 1), (1, −1), (−2,0), (0, 2), (2, 0), (0, −2), (−2, −2), (−2, 2), (2, 2), (2, −2), (−2,−1), (−2, 1), (−1, 2), (1, 2), (2, 1), (2, −1), (1, −2), (−1, −2).
 21. Adecoder, comprising: one or more processors; and a non-transitorycomputer-readable storage medium coupled to the processors and storingprogramming for execution by the processors, the programming, whenexecuted by the processors, configuring the decoder to: obtain aninitial motion vector for a current block; determine search spacepositions according to the initial motion vector; check matching costsfor each of the search space positions according to a checking order toselect a target search space position with a minimal matching cost; anddetermine a refining motion vector of the current block based on theinitial motion vector and the target search space position; wherein acentral search space position is checked first according to the checkingorder, the central search space position being pointed to by the initialmotion vector.